The Elements of Botany, For Beginners and For Schools
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Title: The Elements of Botany, For Beginners and For Schools
Author: Asa Gray
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Language: English
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GRAY'S LESSONS IN BOTANY
REVISED EDITION
THE
ELEMENTS OF BOTANY
FOR BEGINNERS AND FOR SCHOOLS
By ASA GRAY
IVISON, BLAKEMAN, AND COMPANY
NEW YORK AND CHICAGO
_Copyright_,
By Asa Gray.
1887.
PREFACE.
This volume takes the place of the author's Lessons in Botany and
Vegetable Physiology, published over a quarter of a century ago. It is
constructed on the same lines, and is a kind of new and much revised
edition of that successful work. While in some respects more extended,
it is also more concise and terse than its predecessor. This should the
better fit it for its purpose now that competent teachers are common.
They may in many cases develop paragraphs into lectures, and fully
illustrate points which are barely, but it is hoped clearly, stated.
Indeed, even for those without a teacher, it may be that a condensed is
better than a diffuse exposition.
The book is adapted to the higher schools, "How Plants Grow and Behave"
being the "Botany for Young People and Common Schools." It is intended
to ground beginners in Structural Botany and the principles of vegetable
life, mainly as concerns Flowering or Phanerogamous plants, with which
botanical instruction should always begin; also to be a companion and
interpreter to the Manuals and Floras by which the student threads his
flowery way to a clear knowledge of the surrounding vegetable creation.
Such a book, like a grammar, must needs abound in technical words, which
thus arrayed may seem formidable; nevertheless, if rightly apprehended,
this treatise should teach that the study of botany is not the learning
of names and terms, but the acquisition of knowledge and ideas. No
effort should be made to commit technical terms to memory. Any term used
in describing a plant or explaining its structure can be looked up when
it is wanted, and that should suffice. On the other hand, plans of
structure, types, adaptations, and modifications, once understood, are
not readily forgotten; and they give meaning and interest to the
technical terms used in explaining them.
In these "Elements" naturally no mention has been made of certain terms
and names which recent cryptogamically-minded botanists, with lack of
proportion and just perspective, are endeavoring to introduce into
phanerogamous botany, and which are not needed nor appropriate, even in
more advanced works, for the adequate recognition of the ascertained
analogies and homologies.
As this volume will be the grammar and dictionary to more than one or
two Manuals, Floras, etc., the particular directions for procedure which
were given in the "First Lessons" are now relegated to those works
themselves, which in their new editions will provide the requisite
explanations. On the other hand, in view of such extended use, the
Glossary at the end of this book has been considerably enlarged. It will
be found to include not merely the common terms of botanical description
but also many which are unusual or obsolete; yet any of them may now and
then be encountered. Moreover, no small number of the Latin and Greek
words which form the whole or part of the commoner specific names are
added to this Glossary, some in an Anglicized, others in their Latin
form. This may be helpful to students with small Latin and less Greek,
in catching the meaning of a botanical name or term.
The illustrations in this volume are largely increased in number. They
are mostly from the hand of Isaac Sprague.
It happens that the title chosen for this book is that of the author's
earliest publication, in the year 1836, of which copies are rarely seen;
so that no inconvenience is likely to arise from the present use of the
name.
ASA GRAY.
Cambridge, Massachusetts,
_March, 1887_.
CONTENTS.
Page
SECTION I. INTRODUCTORY 9
SECTION II. FLAX AS A PATTERN PLANT 11
Growth from the Seed, Organs of Vegetation 11
Blossoming, Flower, &c. 14
SECTION III. MORPHOLOGY OF SEEDLINGS 15
Germinating Maples 15
Cotyledons thickened, hypogaeous in germination 18
Store of Food external to the Embryo 20
Cotyledons as to number 22
Dicotyledonous and Polycotyledonous 23
Monocotyledonous 24
Simple-stemmed Plants 26
SECTION IV. GROWTH FROM BUDS; BRANCHING 27
Buds, situation and kinds 27
Vigorous vegetation from strong Buds 28
Arrangement of Branches 29
Non-developed, Latent, and Accessory Buds 30
Enumeration of kinds of Buds 31
Definite and Indefinite growth; Deliquescent and Excurrent 31
SECTION V. ROOTS 33
Primary and Secondary. Contrast between Stem and Root 34
Fibrous and Fleshy Roots; names of kinds 34
Anomalous Roots. Epiphytic and Parasitic Plants 36
Duration: Annuals, Biennials, Perennials 37
SECTION VI. STEMS 38
Those above Ground: kinds and modifications 39
Subterranean Stems and Branches 42
Rootstock 42
Tuber 44
Corm 45
Bulb and Bulblets 46
Consolidated Vegetation 47
SECTION VII. LEAVES 49
Sec. 1. LEAVES AS FOLIAGE 49
Parts and Venation 50
Forms as to general outline 52
As to apex and particular outline 53
As to lobing or division 56
Compound, Perfoliate, and Equitant Leaves 57
With no distinction of Petiole and Blade, Phyllodia, &c. 61
Sec. 2. LEAVES OF SPECIAL CONFORMATION AND USE 62
Leaves for storage 62
Leaves as bud-scales 63
Spines 64
and for Climbing 64
Pitchers 64
and Fly-traps 65
Sec. 3. STIPULES 66
Sec. 4. THE ARRANGEMENT OF LEAVES 67
Phyllotaxy 67
Of Alternate Leaves 69
Of Opposite and Whorled Leaves 71
Vernation or Praefoliation 71
SECTION VIII. FLOWERS 72
Sec. 1. POSITION AND ARRANGEMENT, INFLORESCENCE 73
Raceme 73
Corymb, Umbel, Spike, Head 74
Spadix, Catkin, or Ament 75
Panicle: Determinate Inflorescence 76
Cyme, Fascicle, Glomerule, Scorpioid or Helicoid Cymes 77
Mixed Inflorescence 78
Sec. 2. PARTS OR ORGANS OF THE FLOWER 79
Floral Envelopes: Perianth, Calyx, Corolla 79
Essential Organs: Stamen, Pistil 80
Torus or Receptacle 81
Sec. 3. PLAN OF THE FLOWER 81
When perfect, complete, regular, or symmetrical 81
Numerical Plan and Alternation of Organs 82
Flowers are altered branches 83
Sec. 4. MODIFICATIONS OF THE TYPE 85
Unisexual or diclinous 85
Incomplete, Irregular, and Unsymmetrical 86
Flowers with Multiplication of Parts 88
Flowers with Union of Parts: Coalescence 88
Regular Forms 89
Irregular Forms 90
Papilionaceous 91
Labiate 92
and Ligulate Corollas 93
Adnation or Consolidation 94
Position of Flower or of its Parts 96
Sec. 5. ARRANGEMENT OF PARTS IN THE BUD 97
AEstivation or Praefloration, its kinds 97
SECTION IX. STAMENS IN PARTICULAR 98
Androecium 98
Insertion, Relation, &c. 99
Anther and Filament. Pollen 101
SECTION X. PISTILS IN PARTICULAR 105
Sec. 1. ANGIOSPERMOUS OR ORDINARY GYNOECIUM 105
Parts of a complete Pistil 105
Carpels, Simple Pistil 106
Compound Pistil with Cells and Axile Placentae 107
One-celled with Free Central Placenta 108
One-celled with Parietal Placentae 108
Sec. 2. GYMNOSPERMOUS GYNOECIUM 109
SECTION XI. OVULES 110
Their Parts, Insertion, and Kinds 111
SECTION XII. MODIFICATIONS OF THE RECEPTACLE 112
Torus, Stipe, Carpophore, Disk 113
SECTION XIII. FERTILIZATION 114
Sec. 1. ADAPTATIONS FOR POLLINATION OF THE STIGMA 114
Close and Cross Fertilization, Anemophilous and Entomophilous 115
Dichogamy and Heterogony 116
Sec. 2. ACTION OF THE POLLEN AND FORMATION OF THE EMBRYO 117
SECTION XIV. THE FRUIT 117
Nature and kinds 118
Berry, Pepo, Pome 119
Drupe and Akene 120
Cremocarp, Caryopsis, Nut 121
Follicle, Legume, Capsule 122
Capsular Dehiscence, Silique and Silicle 123
Pyxis, Strobile or Cone 124
SECTION XV. THE SEED 125
Seed-coats and their appendages 125
The Kernel or Nucleus, Embryo and its parts, Albumen 127
SECTION XVI. VEGETABLE LIFE AND WORK 128
Sec. 1. ANATOMICAL STRUCTURE AND GROWTH 129
Nature of Growth, Protoplasm 129
Cells and Cell-walls. Cellular Structure or Tissue 130
Strengthening Cells. Wood, Wood-cells, Vessels or Ducts 132
Sec. 2. CELL-CONTENTS 136
Sap, Chlorophyll, Starch 136
Crystals, Rhaphides 137
Sec. 3. ANATOMY OF ROOTS AND STEMS 138
Endogenous and Exogenous Stems 139
Particular structure of the latter 140
Wood, Sapwood and Heart-wood. The living parts of a Tree 141
Sec. 4. ANATOMY OF LEAVES 142
Epidermis, Stomata or Breathing pores 143
Sec. 5. PLANT FOOD AND ASSIMILATION 144
Sec. 6. PLANT WORK AND MOVEMENT 149
Movements in Cells or Cyclosis 149
Transference from Cell to Cell 150
Movements of Organs, Twining Stems, Leaf-movements 150
Movements of Tendrils, Sensitiveness 152
Movements in Flowers 153
Movements for capture of Insects 154
Work costs, using up Material and Energy 155
SECTION XVII. CRYPTOGAMOUS OR FLOWERLESS PLANTS 156
Vascular Cryptogams, Pteridophytes 156
Horsetails (Equisetaceae), Ferns 157
Club-Mosses (Lycopodium), &c. 161
Quillworts (Isoetes), Pillworts (Marsilia) 161
Azolla. Cellular Cryptogams 162
Bryophytes. Mosses (Musci) 163
Liverworts (Hepaticae) 164
Thallophytes 165
Characeae 167
Algae, Seaweeds, &c. 168
Lichenes or Lichens 171
Fungi 172
SECTION XVIII. CLASSIFICATION AND NOMENCLATURE 175
Sec. 1. KINDS AND RELATIONSHIP 175
Species, Varieties, Individuals 176
Genera, Orders, Classes, &c. 177
Sec. 2. NAMES, TERMS AND CHARACTERS 178
Nomenclature of Genera, Species, and Varieties 179
Nomenclature of Orders, Classes, &c. Terminology 180
Sec. 3. SYSTEM 181
Artificial and Natural 182
Synopsis of Series, Classes, &c. 183
SECTION XIX. BOTANICAL WORK 184
Sec. 1. COLLECTION OR HERBORIZATION 184
Sec. 2. HERBARIUM 186
Sec. 3. INVESTIGATION AND DETERMINATION OF PLANTS 187
Sec. 4. SIGNS AND ABBREVIATIONS 188
ABBREVIATIONS OF THE NAMES OF BOTANISTS 190
GLOSSARY COMBINED WITH INDEX 193
ELEMENTS OF BOTANY.
Section I. INTRODUCTORY.
1. BOTANY is the name of the science of the vegetable kingdom in
general; that is, of plants.
2. Plants may be studied as to their kinds and relationships. This study
is SYSTEMATIC BOTANY. An enumeration of the kinds of vegetables, as far
as known, classified according to their various degrees of resemblance
or difference, constitutes a general _System of plants_. A similar
account of the vegetables of any particular country or district is
called a _Flora_.
3. Plants may be studied as to their structure and parts. This is
STRUCTURAL BOTANY, or ORGANOGRAPHY. The study of the organs or parts of
plants in regard to the different forms and different uses which the
same kind of organ may assume,--the comparison, for instance, of a
flower-leaf or a bud-scale with a common leaf,--is VEGETABLE MORPHOLOGY,
or MORPHOLOGICAL BOTANY. The study of the minute structure of the parts,
to learn by the microscope what they themselves are formed of, is
VEGETABLE ANATOMY, or HISTOLOGY; in other words, it is Microscopical
Structural Botany. The study of the actions of plants or of their parts,
of the ways in which a plant lives, grows, and acts, is the province of
PHYSIOLOGICAL BOTANY, or VEGETABLE PHYSIOLOGY.
4. This book is to teach the outlines of Structural Botany and of the
simpler parts of the physiology of plants, that it may be known how
plants are constructed and adapted to their surroundings, and how they
live, move, propagate, and have their being in an existence no less
real, although more simple, than that of the animal creation which they
support. Particularly, this book is to teach the principles of the
structure and relationships of plants, the nature and names of their
parts and their modifications, and so to prepare for the study of
Systematic Botany; in which the learner may ascertain the name and the
place in the system of any or all of the ordinary plants within reach,
whether wild or cultivated. And in ascertaining the name of any plant,
the student, if rightly taught, will come to know all about its general
or particular structure, rank, and relationship to other plants.
5. The vegetable kingdom is so vast and various, and the difference is
so wide between ordinary trees, shrubs, and herbs on the one hand, and
mosses, moulds, and such like on the other, that it is hardly possible
to frame an intelligible account of plants as a whole without
contradictions or misstatements, or endless and troublesome
qualifications. If we say that plants come from seeds, bear flowers, and
have roots, stems, and leaves, this is not true of the lower orders. It
is best for the beginner, therefore, to treat of the higher orders of
plants by themselves, without particular reference to the lower.
6. Let it be understood, accordingly, that there is a higher and a lower
series of plants; namely:--
PHANEROGAMOUS PLANTS, which come from seed and bear _flowers_,
essentially stamens and pistils, through the co-operation of which seed
is produced. For shortness, these are commonly called PHANEROGAMS, or
_Phaenogams_, or by the equivalent English name of FLOWERING PLANTS.[1]
CRYPTOGAMOUS PLANTS, or CRYPTOGAMS, come from minute bodies, which
answer to seeds, but are of much simpler structure, and such plants have
not stamens and pistils. Therefore they are called in English FLOWERLESS
PLANTS. Such are Ferns, Mosses, Algae or Seaweeds, Fungi, etc. These
sorts have each to be studied separately, for each class or order has a
plan of its own.
7. But Phanerogamous, or Flowering, Plants are all constructed on one
plan, or _type_. That is, taking almost any ordinary herb, shrub, or
tree for a pattern, it will exemplify the whole series: the parts of one
plant answer to the parts of any other, with only certain differences in
particulars. And the occupation and the delight of the scientific
botanist is in tracing out this common plan, in detecting the likenesses
under all the diversities, and in noting the meaning of these manifold
diversities. So the attentive study of any one plant, from its growth
out of the seed to the flowering and fruiting state and the production
of seed like to that from which the plant grew, would not only give a
correct general idea of the structure, growth, and characteristics of
Flowering Plants in general, but also serve as a pattern or standard of
comparison. Some plants will serve this purpose of a pattern much better
than others. A proper pattern will be one that is perfect in the sense
of having all the principal parts of a phanerogamous plant, and simple
and regular in having these parts free from complications or disguises.
The common Flax-plant may very well serve this purpose. Being an annual,
it has the advantage of being easily raised and carried in a short time
through its circle of existence, from seedling to fruit and seed.
FOOTNOTES:
[1] The name is sometimes _Phanerogamous_, sometimes _Phaenogamous_
(_Phanerogams_, or _Phaenogams_), terms of the same meaning
etymologically; the former of preferable form, but the latter shorter.
The meaning of such terms is explained in the Glossary.
Section II. FLAX AS A PATTERN PLANT.
8. =Growth from the Seed.= Phanerogamous plants grow from seed, and
their flowers are destined to the production of seeds. A seed has a
rudimentary plant ready formed in it,--sometimes with the two most
essential parts, i. e. stem and leaf, plainly discernible; sometimes
with no obvious distinction of organs until germination begins. This
incipient plant is called an EMBRYO.
9. In this section the Flax-plant is taken as a specimen, or type, and
the development and history of common plants in general is illustrated
by it. In flax-seed the embryo nearly fills the coats, but not quite.
There is a small deposit of nourishment between the seed-coat and the
embryo: this may for the present be left out of the account. This embryo
consists of a pair of leaves, pressed together face to face, and
attached to an extremely short stem. (Fig. 2-4.) In this rudimentary
condition the real nature of the parts is not at once apparent; but when
the seed grows they promptly reveal their character,--as the
accompanying figures (Fig. 5-7) show.
[Illustration: Fig. 1. Pod of Flax. 2. Section lengthwise, showing two
of the seeds; one whole, the other cut half away, bringing contained
embryo into view. 3. Similar section of a flax-seed more magnified and
divided flatwise; turned round, so that the stem-end (caulicle) of the
embryo is below: the whole broad upper part is the inner face of one of
the cotyledons; the minute nick at its base is the plumule. 4. Similar
section through a seed turned edgewise, showing the thickness of the
cotyledons, and the minute plumule between them, i. e. the minute bud on
the upper end of the caulicle.]
10. Before the nature of these parts in the seed was altogether
understood, technical names were given to them, which are still in use.
These initial leaves were named COTYLEDONS. The initial stem on which
they stand was called the RADICLE. That was because it gives rise to the
first root; but, as it is really the beginning of the stem, and because
it is the stem that produces the root and not the root that produces the
stem, it is better to name it the CAULICLE. Recently it has been named
_Hypocotyle_; which signifies something below the cotyledons, without
pronouncing what its nature is.
[Illustration: Fig. 5. Early Flax seedling; stem (caulicle), root at
lower end, expanded seed-leaves (cotyledons) at the other: minute bud
(plumule) between these. 6. Same later; the bud developed into second
pair of leaves, with hardly any stem-part below them; then into a third
pair of leaves, raised on a short joint of stem; and a fifth leaf also
showing. 7. Same still older, with more leaves developed, but these
singly (one after another), and with joints of stem between them.]
11. On committing these seeds to moist and warm soil they soon sprout,
i. e. _germinate_. The very short stem-part of the embryo is the first
to grow. It lengthens, protrudes its root-end; this turns downward, if
not already pointing in that direction, and while it is lengthening a
root forms at its point and grows downward into the ground. This root
continues to grow on from its lower end, and thus insinuates itself and
penetrates into the soil. The stem meanwhile is adding to its length
throughout; it erects itself, and, seeking the light, brings the seed up
out of the ground. The materials for this growth have been supplied by
the cotyledons or seed-leaves, still in the seed: it was the store of
nourishing material they held which gave them their thickish shape, so
unlike that of ordinary leaves. Now, relieved of a part of this store of
food, which has formed the growth by which they have been raised into
the air and light, they appropriate the remainder to their own growth.
In enlarging they open and throw off the seed-husk; they expand, diverge
into a horizontal position, turn green, and thus become a pair of
evident leaves, the first foliage of a tiny plant. This seedling,
although diminutive and most simple, possesses and puts into use, all
the ORGANS of VEGETATION, namely, root, stem, and leaves, each in its
proper element,--the root in the soil, the stem rising out of it, the
leaves in the light and open air. It now draws in moisture and some
food-materials from the soil by its root, conveys this through the stem
into the leaves, where these materials, along with other crude food
which these imbibe from the air, are assimilated into vegetable matter,
i. e. into the material for further growth.
12. =Further Growth= soon proceeds to the formation of new
parts,--downward in the production of more root, or of branches of the
main root, upward in the development of more stem and leaves. That from
which a stem with its leaves is continued, or a new stem (i. e. branch)
originated, is a BUD. The most conspicuous and familiar buds are those
of most shrubs and trees, bearing buds formed in summer or autumn, to
grow the following spring. But every such point for new growth may
equally bear the name. When there is such a bud between the cotyledons
in the seed or seedling it is called the PLUMULE. This is conspicuous
enough in a bean (Fig. 29.), where the young leaf of the new growth
looks like a little plume, whence the name, _plumule_. In flax-seed this
is very minute indeed, but is discernible with a magnifier, and in the
seedling it shows itself distinctly (Fig. 5, 6, 7).
13. As it grows it shapes itself into a second pair of leaves, which of
course rests on a second joint of stem, although in this instance that
remains too short to be well seen. Upon its summit appears the third
pair of leaves, soon to be raised upon its proper joint of stem; the
next leaf is single, and is carried up still further upon its supporting
joint of stem; and so on. The root, meanwhile, continues to grow
underground, not joint after joint, but continuously, from its lower
end; and commonly it before long multiplies itself by branches, which
lengthen by the same continuous growth. But stems are built up by a
succession of leaf-bearing growths, such as are strongly marked in a
reed or corn-stalk, and less so in such an herb as Flax. The word
"joint" is ambiguous: it may mean either the portion between successive
leaves, or their junction, where the leaves are attached. For precision,
therefore, the place where the leaf or leaves are borne is called a
NODE, and the naked interval between two nodes, an INTERNODE.
[Illustration: Fig. 8. Upper part of Flax-plant in blossom.]
14. In this way a simple stem with its garniture of leaves is developed
from the seed. But besides this direct continuation, buds may form and
develop into lateral stems, that is, _into branches_, from any node. The
proper origin of branches is from the AXIL of a leaf, i. e. the angle
between leaf and stem on the upper side; and branches may again branch,
so building up the herb, shrub, or tree. But sooner or later, and
without long delay in an annual like Flax, instead of this continuance
of mere vegetation, reproduction is prepared for by
15. =Blossoming.= In Flax the flowers make their appearance at the end
of the stem and branches. The growth, which otherwise might continue
them farther or indefinitely, now takes the form of blossom, and is
subservient to the production of seed.
[Illustration: Fig. 9. Flax-flowers about natural size. 10. Section of a
flower moderately enlarged, showing a part of the petals and stamens,
all five styles, and a section of ovary with two ovules or rudimentary
seeds.]
16. =The Flower= of Flax consists, first, of five small green leaves,
crowded into a circle: this is the CALYX, or flower-cup. When its
separate leaves are referred to they are called SEPALS, a name which
distinguishes them from foliage-leaves on the one hand, and from petals
on the other. Then come five delicate and _colored_ leaves (in the Flax,
blue), which form the COROLLA, and its leaves are PETALS; then a circle
of organs, in which all likeness to leaves is lost, consisting of
slender stalks with a knob at summit, the STAMENS; and lastly, in the
centre, the rounded body, which becomes a pod, surmounted by five
slender or stalk-like bodies. This, all together, is the PISTIL. The
lower part of it, which is to contain the seeds, is the OVARY; the
slender organs surmounting this are STYLES; the knob borne on the apex
of each style is a STIGMA. Going back to the stamens, these are of two
parts, viz. the stalk, called FILAMENT, and the body it bears, the
ANTHER. Anthers are filled with POLLEN, a powdery substance made up of
minute grains.
17. The pollen shed from the anthers when they open falls upon or is
conveyed to the stigmas; then the pollen-grains set up a kind of growth
(to be discerned only by aid of a good microscope), which penetrates the
style: this growth takes the form of a thread more delicate than the
finest spider's web, and reaches the bodies which are to become seeds
(OVULES they are called until this change occurs); these, touched by
this influence, are incited to a new growth within, which becomes an
embryo. So, as the ovary ripens into the seed-pod or capsule (Fig. 1,
etc.) containing seeds, each seed enclosing a rudimentary new plantlet,
the round of this vegetable existence is completed.
Section III. MORPHOLOGY OF SEEDLINGS.
18. Having obtained a general idea of the growth and parts of a
phanerogamous plant from the common Flax of the field, the seeds and
seedlings of other familiar plants may be taken up, and their variations
from the assumed pattern examined.
19. =Germinating Maples= are excellent to begin with, the parts being so
much larger than in Flax that a common magnifying glass, although
convenient, is hardly necessary. The only disadvantage is that fresh
seeds are not readily to be had at all seasons.
[Illustration: Fig. 11. Embryo of Sugar Maple, cut through lengthwise
and taken out of the seed. 12, 13. Whole embryo of same just beginning
to grow; _a_, the stemlet or caulicle, which in 13 has considerably
lengthened.]
20. The seeds of Sugar Maple ripen at the end of summer, and germinate
in early spring. The embryo fills the whole seed, in which it is nicely
packed; and the nature of the parts is obvious even before growth
begins. There is a stemlet (caulicle) and a pair of long and narrow
seed-leaves (cotyledons), doubled up and coiled, green even in the seed,
and in germination at once unfolding into the first pair of
foliage-leaves, though of shape quite unlike those that follow.
21. Red Maple seeds are ripe and ready to germinate at the beginning of
summer, and are therefore more convenient for study. The cotyledons are
crumpled in the seed, and not easy to straighten out until they unfold
themselves in germination. The story of their development into the
seedling is told by the accompanying Fig. 14-20; and that of Sugar Maple
is closely similar. No plumule or bud appears in the embryo of these two
Maples until the seed-leaves have nearly attained their full growth and
are acting as foliage-leaves, and until a root is formed below. There is
no great store of nourishment in these thin cotyledons; so further
growth has to wait until the root and seed-leaves have collected and
elaborated sufficient material for the formation of the second internode
and its pair of leaves, which lending their help the third pair is more
promptly produced, and so on.
22. Some change in the plan comes with the Silver or Soft White Maple.
(Fig. 21-25). This blossoms in earliest spring, and it drops its large
and ripened keys only a few weeks later. Its cotyledons have not at all
the appearance of leaves; they are short and broad, and (as there is no
room to be saved by folding) they are straight, except a small fold at
the top,--a vestige of the habit of Maples in general. Their unusual
thickness is due to the large store of nutritive matter they contain,
and this prevents their developing into actual leaves. Correspondingly,
their caulicle does not lengthen to elevate them above the surface of
the soil; the growth below the cotyledons is nearly all of root. It is
the little plumule or bud between them which makes the upward growth,
and which, being well fed by the cotyledons, rapidly develops the next
pair of leaves and raises them upon a long internode, and so on. The
cotyledons all the while remain below, in the husk of the fruit and
seed, and perish when they have yielded up the store of food which they
contained.
[Illustration: Fig. 14. One of the pair of keys or winged fruits of Red
Maple; the seed-bearing portion cut open to show the seed. 15. Seed
enlarged, and divided to show the crumpled embryo which fills it. 16.
Embryo taken out and partly opened. 17. Embryo which has unfolded in
early stage of germination and begun to grow. 18. Seedling with next
joint of stem and leaves apparent; and 19 with these parts full-grown,
and bud at apex for further growth. 20. Seedling with another joint of
stem and pair of leaves.]
23. So, even in plants so much alike as Maples, there is considerable
difference in the amount of food stored up in the cotyledons by which
the growth is to be made; and there are corresponding differences in the
germination. The larger the supply to draw upon, the stronger the
growth, and the quicker the formation of root below and of stem and
leaves above. This deposit of food thickens the cotyledons, and renders
them less and less leaf-like in proportion to its amount.
[Illustration: Fig. 21. Fruit (one key) of Silver Maple, Acer
dasycarpum, of natural size, the seed-bearing portion divided to show
the seed. 22. Embryo of the seed taken out. 23. Same opened out, to show
the thick cotyledons and the little plumule or bud between them. 24.
Germination of Silver Maple, natural size; merely the base of the fruit,
containing the seed, is shown. 25. Embryo of same, taken out of the
husk; upper part of growing stem cut off, for want of room.]
24. =Examples of Embryos with thickened Cotyledons.= In the Pumpkin and
Squash (Fig. 26, 27), the cotyledons are well supplied with nourishing
matter, as their sweet taste demonstrates. Still, they are flat and not
very thick. In germination this store is promptly utilized in the
development of the caulicle to twenty or thirty times its length in the
seed, and to corresponding thickness, in the formation of a cluster of
roots at its lower end, and the early production of the incipient
plumule; also in their own growth into efficient green leaves. The case
of our common Bean (Phaseolus vulgaris, Fig. 28-30) is nearly the same,
except that the cotyledons are much more gorged; so that, although
carried up into the air and light upon the lengthening caulicle, and
there acquiring a green color, they never expand into useful leaves.
Instead of this, they nourish into rapid growth the plumule, which is
plainly visible in the seed, as a pair of incipient leaves; and these
form the first actual foliage.
25. Very similar is the germination of the Beech (Fig. 31-33), except
that the caulicle lengthens less, hardly raising the cotyledons out of
the ground. Nothing would be gained by elevating them, as they never
grow out into efficient leaves; but the joint of stem belonging to the
plumule lengthens well, carrying up its pair of real foliage-leaves.
26. It is nearly the same in the Bean of the Old World (Vicia Faba, here
called Horse Bean and Windsor Bean): the caulicle lengthens very little,
does not undertake to elevate the heavy seed, which is left below or
upon the surface of the soil, the flat but thick cotyledons remaining
in it, and supplying food for the growth of the root below and the
plumule above. In its near relative, the Pea (Fig. 34, 35), this use of
cotyledons for storage only is most completely carried out. For they are
thickened to the utmost, even into hemispheres; the caulicle does not
lengthen at all; merely sends out roots from the lower end, and develops
its strong plumule from the upper, the seed remaining unmoved
underground. That is, in technical language, the germination is
_hypogaeous_.
[Illustration: Fig. 26. Embryo of Pumpkin-seed, partly opened. 27. Young
seedling of same.]
[Illustration: Fig. 28. Embryo of Common Bean (Phaseolus vulgaris):
caulicle bent down over edge of cotyledons. 29. Same germinating:
caulicle well lengthened and root beginning; thick cotyledons partly
spreading; and plumule (pair of leaves) growing between them. 30. Same,
older, with plumule developed into internode and pair of leaves.]
27. There is sufficient nourishment in the cotyledons of a pea to make a
very considerable growth before any actual foliage is required. So it is
the stem-portion of the plumule which is at first conspicuous and
strong-growing. Here, as seen in Fig. 35, its lower nodes bear each a
useless leaf-scale instead of an efficient leaf, and only the later ones
bear leaves fitted for foliage.
[Illustration: Fig. 31. A Beech-nut, cut across. 32. Beginning
germination of the Beech, showing the plumule growing before the
cotyledons have opened or the root has scarcely formed. 33. The same, a
little later, with the plumule-leaves developing, and elevated on a long
internode.]
[Illustration: Fig. 34. Embryo of Pea, i. e. a pea with the coats
removed; the short and thick caulicle presented to view. 35. Same in
advanced germination: the plumule has developed four or five internodes,
bearing single leaves; but the first and second leaves are mere scales,
the third begins to serve as foliage; the next more so.]
28. This _hypogaeous_ germination is exemplified on a larger scale by the
Oak (Fig. 36, 37) and Horse-chestnut (Fig. 38, 39); but in these the
downward growth is wholly a stout tap-root. It is not the caulicle; for
this lengthens hardly any. Indeed, the earliest growth which carries the
very short caulicle out of the shell comes from the formation of
foot-stalks to the cotyledons; above these develops the strong plumule,
below grows the stout root. The growth is at first entirely, for a long
time mainly, at the expense of the great store of food in the
cotyledons. These, after serving their purpose, decay and fall away.
[Illustration: Fig. 36. Half of an acorn, cut lengthwise, filled by the
very thick cotyledons, the base of which encloses the minute caulicle.
37. Oak-seedling.]
[Illustration: Fig. 38. Half of a horse-chestnut, similarly cut; the
caulicle is curved down on the side of one of the thick cotyledons. 39.
Horse-chestnut in germination; foot-stalks are formed to the cotyledons,
pushing out in their lengthening the growing parts.]
29. Such thick cotyledons never separate; indeed, they sometimes grow
together by some part of their contiguous faces; so that the germination
seems to proceed from a solid bulb-like mass. This is the case in a
horse-chestnut.
30. =Germinating Embryo supplied by its own Store of Nourishment=, i. e.
the store in the cotyledons. This is so in all the illustrations thus
far, essentially so even in the Flax. This nourishment was supplied by
the mother plant to the ovule and seed, and thence taken into the embryo
during its growth. Such embryos, filling the whole seed, are
comparatively large and strong, and vigorous in germination in
proportion to the amount of their growth while connected with the parent
plant.
31. =Germinating Embryo supplied from a Deposit outside of Itself.= This
is as common as the other mode; and it occurs in all degrees. Some
seeds have very little of this deposit, but a comparatively large
embryo, with its parts more or less developed and recognizable. In
others this deposit forms the main bulk of the seed, and the embryo is
small or minute, and comparatively rudimentary. The following
illustrations exemplify these various grades. When an embryo in a seed
is thus surrounded by a white substance, it was natural to liken the
latter to the white of an egg, and the embryo or germ to the yolk. So
the matter around or by the side of the embryo was called the _Albumen_,
i. e. the white of the seed. The analogy is not very good; and to avoid
ambiguity some botanists call it the ENDOSPERM. As that means in English
merely the inwards of a seed, the new name is little better than the old
one; and, since we do not change names in botany except when it cannot
be avoided, this name of _albumen_ is generally kept up. A seed with
such a deposit is _albuminous_, one with none is _exalbuminous_.
32. The ALBUMEN forms the main bulk of the seed in wheat, maize, rice,
buckwheat, and the like. It is the floury part of the seed. Also of the
cocoa-nut, of coffee (where it is dense and hard), etc.; while in peas,
beans, almonds, and in most edible nuts, the store of food, although
essentially the same in nature and in use, is in the embryo itself, and
therefore is not counted as anything to be separately named. In both
forms this concentrated food for the germinating plant is food also for
man and for animals.
[Illustration: Fig. 40. Seed of Morning Glory divided, moderately
magnified; shows a longitudinal section through the centre of the embryo
as it lies crumpled in the albumen. 41. Embryo taken out whole and
unfolded; the broad and very thin cotyledons notched at summit; the
caulicle below. 42. Early state of germination. 43. Same, more advanced;
caulicle or primary stem, cotyledons or seed-leaves, and below, the
root, well developed.]
33. For an albuminous seed with a well-developed embryo, the common
Morning Glory (Ipomoea purpurea, Fig. 40-43) is a convenient example,
being easy and prompt to grow, and having all the parts well apparent.
The seeds (duly soaked for examination) and the germination should be
compared with those of Sugar and Red Maple (19-21). The only essential
difference is that here the embryo is surrounded by and crumpled up in
the albumen. This substance, which is pulpy or mucilaginous in fresh and
young seeds, hardens as the seed ripens, but becomes again pulpy in
germination; and, as it liquefies, the thin cotyledons absorb it by
their whole surface. It supplements the nutritive matter contained in
the embryo. Both together form no large store, but sufficient for
establishing the seedling, with tiny root, stem, and pair of leaves for
initiating its independent growth; which in due time proceeds as in Fig.
44, 45.
[Illustration: Fig. 44. Seedling of Morning Glory more advanced (root
cut away); cotyledons well developed into foliage-leaves: succeeding
internode and leaf well developed, and the next forming. 45. Seedling
more advanced; reduced to much below natural size.]
34. Smaller embryos, less developed in the seed, are more dependent upon
the extraneous supply of food. The figures 46-53 illustrate four grades
in this respect. The smallest, that of the Peony, is still large enough
to be seen with a hand magnifying glass, and even its cotyledons may be
discerned by the aid of a simple stage microscope.
35. The broad cotyledons of Mirabilis, or Four-o'clock (Fig. 52, 53),
with the slender caulicle almost encircle and enclose the floury
albumen, instead of being enclosed in it, as in the other illustrations.
Evidently here the germinating embryo is principally fed by one of the
leaf-like cotyledons, the other being out of contact with the supply. In
the embryo of Abronia (Fig. 54, 55), a near relative of Mirabilis, there
is a singular modification; one cotyledon is almost wanting, being
reduced to a rudiment, leaving it for the other to do the work. This
leads to the question of the
36. =Number of Cotyledons.= In all the preceding illustrations, the
embryo, however different in shape and degree of development, is
evidently constructed upon one and the same plan, namely, that of two
leaves on a caulicle or initial stem,--a plan which is obvious even when
one cotyledon becomes very much smaller than the other, as in the rare
instance of Abronia (Fig. 54, 55). In other words, the embryos so far
examined are all
37. =Dicotyledonous=, that is, two-cotyledoned. Plants which are thus
similar in the plan of the embryo agree likewise in the general
structure of their stems, leaves, and blossoms; and thus form a class,
named from their embryo DICOTYLEDONES, or in English, DICOTYLEDONOUS
PLANTS. So long a name being inconvenient, it may be shortened into
DICOTYLS.
[Illustration: Fig. 46. Section of a seed of a Peony, showing a very
small embryo in the albumen, near one end. 47. This embryo detached, and
more magnified.]
[Illustration: Fig. 48. Section of a seed of Barberry, showing the
straight embryo in the middle of the albumen. 49. Its embryo detached.]
[Illustration: Fig. 50. Section of a Potato seed, showing the embryo
coiled in the albumen. 51. Its embryo detached.]
[Illustration: Fig. 52. Section of the seed of Mirabilis or
Four-o'clock, showing the embryo coiled round the outside of the
albumen. 53. Embryo detached; showing the very broad and leaf-like
cotyledons, applied face to face, and the pair incurved.]
[Illustration: Fig. 54. Embryo of Abronia umbellata; one of the
cotyledons very small. 55. Same straightened out.]
38. =Polycotyledonous= is a name employed for the less usual case in
which there are more than two cotyledons. The Pine is the most familiar
case. This occurs in all Pines, the number of cotyledons varying from
three to twelve; in Fig. 56, 57 they are six. Note that they are all on
the same level, that is, belong to the same node, so as to form a circle
or _whorl_ at the summit of the caulicle. When there are only three
cotyledons, they divide the space equally, are one third of the circle
apart. When only two they are 180 deg. apart, that is, are _opposite_.
39. The case of three or more cotyledons, which is constant in Pines and
in some of their relatives (but not in all of them), is occasional among
Dicotyls. And the polycotyledonous is only a variation of the
dicotyledonous type,--a difference in the number of leaves in the whorl;
for a pair is a whorl reduced to two members. Some suppose that there
are really only two cotyledons even in a Pine embryo, but these divided
or split up congenitally so as to imitate a greater number. But as
leaves are often in whorls on ordinary stems, they may be so at the very
beginning.
[Illustration: Fig. 56. Section of a Pine-seed, showing its
polycotyledonous embryo in the centre of the albumen, moderately
magnified. 57. Seedling of same, showing the freshly expanded six
cotyledons in a whorl, and the plumule just appearing.]
40. =Monocotyledonous= (meaning with single cotyledon) is the name of
the one-cotyledoned sort of embryo. This goes along with peculiarities
in stem, leaves, and flowers, which all together associate such plants
into a great class, called MONOCOTYLEDONOUS PLANTS, or, for shortness,
MONOCOTYLS. It means merely that the leaves are alternate from the very
first.
[Illustration: Fig. 58. Section of a seed of the Iris, or
Flower-de-Luce, enlarged, showing its small embryo in the albumen, near
the bottom. 59. A germinating seedling of the same, its plumule
developed into the first four leaves (alternate), the first one
rudimentary, the cotyledon remains in the seed.]
41. In Iris (Fig. 58, 59) the embryo in the seed is a small cylinder at
one end of the mass of the albumen, with no apparent distinction of
parts. The end which almost touches the seed coat is caulicle, the other
end belongs to the solitary cotyledon. In germination the whole
lengthens (but mainly the cotyledon) only enough to push the proximate
end fairly out of the seed; from this end the root is formed, and from a
little higher the plumule later emerges. It would appear therefore that
the cotyledon answers to a minute leaf rolled up, and that a chink
through which the plumule grows out is a part of the inrolled edges. The
embryo of Indian Corn shows these parts on a larger scale and in a more
open state (Fig. 66-68). There, in the seed, the cotyledon remains,
imbibing nourishment from the softened albumen, and transmitting it to
the growing root below and new-forming leaves above.
[Illustration: Fig. 60. Section of an Onion seed showing the slender and
coiled embryo in the albumen, moderately magnified. 61. Seed of same in
early germination.]
[Illustration: Fig. 62. Germinating Onion, more advanced, the chink at
base of cotyledon opening for the protrusion of the plumule, consisting
of a thread-shaped leaf. 63. Section of base of Fig. 62, showing plumule
enclosed. 64. Section of same later, plumule emerging. 65. Later stage
of 62, upper part cut off. 66. A grain of Indian Corn, flatwise, cut
away a little, so as to show the embryo, lying on the albumen which
makes the principal bulk of the seed. 67. A grain cut through the middle
in the opposite direction, dividing the embryo through its thick
cotyledon and its plumule, the latter consisting of two leaves, one
enclosing the other. 68. The embryo taken out whole; the thick mass is
the cotyledon, the narrow body partly enclosed by it is the plumule, the
little projection at its base is the very short radicle enclosed in the
sheathing base of the first leaf of the plumule.]
[Illustration: Fig. 69. Grain of Indian Corn in germination, the
ascending sprout is the first leaf of the plumule, enclosing the younger
leaves within, at its base the primary root has broken through. 70. The
same, advanced; the second and third leaves developing, while the
sheathing first leaf does not further develop.]
42. The general plan is the same in the Onion (Fig. 60-65), but with a
striking difference. The embryo is long, and coiled in the albumen of
the seed. To ordinary examination it shows no distinction of parts. But
germination plainly shows that all except the lower end of it is
cotyledon. For after it has lengthened into a long thread, the chink
from which the plumule in time emerges is seen at the base, or near it,
so the caulicle is extremely short, and does not elongate, but sends out
from its base a simple root, and afterwards others in a cluster. Not
only does the cotyledon lengthen enormously in the seedling, but (unlike
that of Iris, Indian Corn, and all the cereal grains) it raises the
comparatively light seed into the air, the tip still remaining in the
seed and feeding upon the albumen. When this food is exhausted and the
seedling is well established in the soil, the upper end decays and the
emptied husk of the seed falls away.
43. In Maize or Indian Corn (Fig. 66-70), the embryo is more developed
in the seed, and its parts can be made out. It lies against the starchy
albumen, but is not enclosed therein. The larger part of it is the
cotyledon, thickish, its edges involute, and its back in contact with
the albumen; partly enclosed by it is the well-developed plumule or bud
which is to grow. For the cotyledon remains in the seed to fulfil its
office of imbibing nourishment from the softened albumen, which it
conveys to the growing sprout; the part of this sprout which is visible
is the first leaf of the plumule rolled up into a sheath and enclosing
the rudiments of the succeeding leaves, at the base enclosing even the
minute caulicle. In germination the first leaf of the plumule develops
only as a sort of sheath, protecting the tender parts within; the second
and the third form the first foliage. The caulicle never lengthens: the
first root, which is formed at its lower end, or from any part of it,
has to break through the enclosing sheath; and succeeding roots soon
spring from all or any of the nodes of the plumule.
44. =Simple-stemmed Plants= are thus built up, by the continuous
production of one leaf-bearing portion of stem from the summit of the
preceding one, beginning with the initial stem (or caulicle) in the
embryo. Some Dicotyls and many Monocotyls develop only in this single
line of growth (as to parts above ground) until the flowering state is
approached. For some examples, see Cycas (Fig. 71, front, at the left);
a tall Yucca or Spanish Bayonet, and two Cocoa-nut Palms behind; at the
right, a group of Sugar-canes, and a Banana behind.
[Illustration: Fig. 71. Simple-stemmed vegetation.]
Section IV. GROWTH FROM BUDS: BRANCHING.
45. Most plants increase the amount of their vegetation by branching,
that is, by producing lateral shoots.
46. Roots branch from any part and usually without definite order. Stems
normally give rise to branches only at definite points, namely, at the
nodes, and there only from the axils of leaves.
47. =Buds= (Fig. 72, 73). Every incipient shoot is a _Bud_ (12). A stem
continues its growth by its _terminal bud_; it branches by the formation
and development of _lateral buds_. As normal lateral buds occupy the
axils of leaves, they are called _axillary buds_. As leaves are
symmetrically arranged on the stem, the buds in their axils and the
branches into which axillary buds grow partake of this symmetry. The
most conspicuous buds are the scaly winter-buds of most shrubs and trees
of temperate and cold climates; but the name belongs as well to the
forming shoot or branch of any herb.
[Illustration: Fig. 72. Shoot of Horse-chestnut, of one year's growth,
taken in autumn after the leaves have fallen; showing the large terminal
bud and smaller axillary buds.]
[Illustration: Fig. 73. Similar shoot of Shagbark Hickory, Carya alba.]
48. =The Terminal Bud=, in the most general sense, may be said to exist
in the embryo,--as cotyledons, or the cotyledons and plumule,--and to
crown each successive growth of the simple stem so long as the summit is
capable of growth. The whole ascending growth of the Palm, Cycas, and
the like (such as in Fig. 71) is from a terminal bud. Branches, being
repetitions of the main stem and growing in the same way, are also
lengthened by terminal buds. Those of Horse-chestnut, Hickory, Maples,
and such trees, being the resting buds of winter, are conspicuous by
their protective covering of scales. These bud-scales, as will hereafter
be shown, are themselves a kind of leaves.
49. =Axillary Buds= were formed on these annual shoots early in the
summer. Occasionally they grow the same season into branches; at least,
some of them are pretty sure to do so whenever the growing terminal bud
at the end of the shoot is injured or destroyed. Otherwise they may lie
dormant until the following spring. In many trees or shrubs these
axillary buds do not show themselves until spring; but if searched for,
they may be detected, though of small size, hidden under the bark.
Sometimes, although early formed, they are concealed all summer long
under the base of the leaf-stalk, which is then hollowed out into a sort
of inverted cup, like a candle-extinguisher, to cover them; as in the
Locust, the Yellow-wood, or more strikingly in the Button-wood or
Plane-tree (Fig. 74).
[Illustration: Fig. 74. An axillary bud, concealed under the hollowed
base of the leaf-stalk, in Buttonwood or Plane-tree.]
50. The _leaf-scars_, so conspicuous in Fig. 72, 73, under each axillary
bud, mark the place where the stalk of the subtending leaf was attached
until it fell in autumn.
51. =Scaly Buds=, which are well represented in Fig. 72, 73, commonly
belong to trees and shrubs of countries in which growth is suspended
during winter. The scaly coverings protect the tender young parts
beneath, not so much by keeping out the cold, which of course would
penetrate the bud in time, as by shielding the interior from the effects
of sudden changes. There are all gradations between these and
52. =Naked Buds=, in which these scales are inconspicuous or wanting, as
in most herbs, at least above ground, and most tropical trees and
shrubs. But nearly related plants of the same climate may differ widely
in this respect. Rhododendrons have strong and scaly winter-buds; while
in Kalmia they are naked. One species of Viburnum, the Hobble-bush, has
completely naked buds, what would be a pair of scales developing into
the first leaves in spring; while another (the Snowball) has conspicuous
scaly buds.
53. =Vigor of Vegetation from strong buds.= Large and strong buds, like
those of the Horse-chestnut, Hickory, and the like, contain several
leaves, or pairs of leaves, ready formed, folded and packed away in
small compass, just as the seed-leaves of a strong embryo are packed
away in the seed: they may even contain all the blossoms of the ensuing
season, plainly visible as small buds. And the stems upon which these
buds rest are filled with abundant nourishment, which was deposited the
summer before in the wood or in the bark. Under the surface of the
soil, or on it covered with the fallen leaves of autumn, similar strong
buds of our perennial herbs may be found; while beneath are thick roots,
rootstocks, or tubers, charged with a great store of nourishment for
their use. This explains how it is that vegetation from such buds shoots
forth so vigorously in the spring of the year, and clothes the bare and
lately frozen surface of the soil, as well as the naked boughs of trees,
very promptly with a covering of fresh green, and often with brilliant
blossoms. Everything was prepared, and even formed, beforehand: the
short joints of stem in the bud have only to lengthen, and to separate
the leaves from each other so that they may unfold and grow. Only a
small part of the vegetation of the season comes directly from the seed,
and none of the earliest vernal vegetation. This is all from buds which
have lived through the winter.
54. =The Arrangement of Branches=, being that of axillary buds, answers
to that of the leaves. Now leaves principally are either _opposite_ or
_alternate_. Leaves are _opposite_ when there are two from the same
joint of stem, as in Maples (Fig. 20), the two being on opposite sides
of the stem; and so the axillary buds and branches are opposite, as in
Fig. 75. Leaves are _alternate_ when there is only one from each joint
of stem, as in the Oak, Lime-tree, Poplar, Button-wood (Fig. 74),
Morning-Glory (Fig. 45,--not counting the seed-leaves, which of course
are opposite, there being a pair of them); also in Indian Corn (Fig.
70), and Iris (Fig. 59). Consequently the axillary buds are also
alternate, as in Hickory (Fig. 73); and the branches they form
alternate,--making a different kind of spray from the other mode, one
branch shooting on one side of the stem and the next on some other. For
in the alternate arrangement no leaf is on the same side of the stem as
the one next above or next below it.
55. But the symmetry of branches (unlike that of the leaves) is rarely
complete. This is due to several causes, and most commonly to the
56. =Non-development of buds.= It never happens that all the buds grow.
If they did, there might be as many branches in any year as there were
leaves the year before. And of those which do begin to grow, a large
portion perish, sooner or later, for want of nourishment, or for want of
light, or because those which first begin to grow have an advantage,
which they are apt to keep, taking to themselves the nourishment of the
stem, and starving the weaker buds. In the Horse-chestnut (Fig. 72),
Hickory (Fig. 73), Magnolia, and most other trees with large scaly buds,
the terminal bud is the strongest, and has the advantage in growth; and
next in strength are the upper axillary buds: while the former continues
the shoot of the last year, some of the latter give rise to branches,
and the rest fail to grow. In the Lilac also (Fig. 75), the uppermost
axillary buds are stronger than the lower; but the terminal bud rarely
appears at all; in its place the uppermost pair of axillary buds grow,
and so each stem branches every year into two,--making a repeatedly
two-forked ramification, as in Fig. 76.
[Illustration: Fig. 75. Shoot of Lilac, with winter buds; the two
uppermost axillary ones strong; the terminal not developed. 76. Forking
ramification of Lilac; reduced in size.]
57. =Latent Buds.= Axillary buds that do not grow at the proper season,
and especially those which make no appearance externally, may long
remain latent, and at length upon a favorable occasion start into
growth, so forming branches apparently out of place as they are out of
time. The new shoots seen springing directly out of large stems may
sometimes originate from such latent buds, which have preserved their
life for years. But commonly these arise from
58. =Adventitious Buds.= These are buds which certain shrubs and trees
produce anywhere on the surface of the wood, especially where it has
been injured. They give rise to the slender twigs which often feather
the sides of great branches of our American Elms. They sometimes form on
the root, which naturally is destitute of buds; they are even found upon
some leaves; and they are sure to appear on the trunks and roots of
Willows, Poplars, and Chestnuts, when these are wounded or mutilated.
Indeed Osier-Willows are _pollarded_, or cut off, from time to time, by
the cultivator, for the purpose of producing a crop of slender
adventitious twigs, suitable for basket-work. Such branches, being
altogether irregular, of course interfere with the natural symmetry of
the tree. Another cause of irregularity, in certain trees and shrubs, is
the formation of what are called
[Illustration: Fig. 77. Tartarean Honeysuckle, with three accessory buds
in each axil.]
59. =Accessory or Supernumerary Buds.= There are cases where two, three,
or more buds spring from the axil of a leaf, instead of the single one
which is ordinarily found there. Sometimes they are placed one over the
other, as in the Aristolochia or Pipe-Vine, and in the Tartarean
Honeysuckle (Fig. 77); also in the Honey-Locust, and in the Walnut and
Butternut (Fig. 78), where the upper supernumerary bud is a good way
out of the axil and above the others. And this is here stronger than the
others, and grows into a branch which is considerably out of the axil,
while the lower and smaller ones commonly do not grow at all. In other
cases three buds stand side by side in the axil, as in the Hawthorn, and
the Red Maple (Fig. 79.) If these were all to grow into branches, they
would stifle each other. But some of them are commonly flower-buds: in
the Red Maple, only the middle one is a leaf-bud, and it does not grow
until after those on each side of it have expanded the blossoms they
contain.
[Illustration: Fig. 78. Butternut branch, with accessory buds, the
uppermost above the axil.]
[Illustration: Fig. 79. Red-Maple branch, with accessory buds placed
side by side. The annular lines toward the base in this and in Fig. 72
are scars of the bud-scales, and indicate the place of the winter-bud of
the preceding year.]
60. =Sorts of Buds.= It may be useful to enumerate the kinds of buds
which have been described or mentioned. They are
_Terminal_, when they occupy the summit of (or terminate) a stem,
_Lateral_, when they are borne on the side of a stem; of which the
regular kind is the
_Axillary_, situated in the axil of a leaf. These are
_Accessory_ or _Supernumerary_, when they are in addition to the normal
solitary bud; and these are _Collateral_, when side by side;
_Superposed_, when one above another;
_Extra-axillary_, when they appear above the axil, as some do when
superposed, and as occasionally is the case when single.
_Naked buds_; those which have no protecting scales.
_Scaly buds_; those which have protecting scales, which are altered
leaves or bases of leaves.
_Leaf-buds_, contain or give rise to leaves, and develop into a leafy
shoot.
_Flower-buds_, contain or consist of blossoms, and no leaves.
_Mixed buds_, contain both leaves and blossoms.
61. =Definite annual Growth= from winter buds is marked in most of the
shoots from strong buds, such as those of the Horse-chestnut and Hickory
(Fig. 72, 73). Such a bud generally contains, already formed in
miniature, all or a great part of the leaves and joints of stem it is to
produce, makes its whole growth in length in the course of a few weeks,
or sometimes even in a few days, and then forms and ripens its buds for
the next year's similar growth.
62. =Indefinite annual Growth=, on the other hand, is well marked in
such trees or shrubs as the Honey-Locust, Sumac, and in sterile shoots
of the Rose, Blackberry, and Raspberry. That is, these shoots are apt
to grow all summer long, until stopped by the frosts of autumn or some
other cause. Consequently they form and ripen no terminal bud protected
by scales, and the upper axillary buds are produced so late in the
season that they have no time to mature, nor has their wood time to
solidify and ripen. Such stems therefore commonly die back from the top
in winter, or at least all their upper buds are small and feeble; so the
growth of the succeeding year takes place mainly from the lower axillary
buds, which are more mature.
63. =Deliquescent and Excurrent Growth.= In the former case, and
wherever axillary buds take the lead, there is, of course, no single
main stem, continued year after year in a direct line, but the trunk is
soon lost in the branches. Trees so formed commonly have rounded or
spreading tops. Of such trees with _deliquescent_ stems,--that is, with
the trunk dissolved, as it were, into the successively divided
branches,--the common American Elm (Fig. 80) is a good illustration.
[Illustration: Fig. 80. An American Elm, with Spruce-trees, and on the
left Arbor Vitae.]
64. On the other hand, the main stem of Firs and Spruces, unless
destroyed by some injury, is carried on in a direct line throughout the
whole growth of the tree, by the development year after year of a
terminal bud: this forms a single, uninterrupted shaft,--an _excurrent_
trunk, which cannot be confounded with the branches that proceed from
it. Of such _spiry_ or _spire-shaped_ trees, the Firs or Spruces are
characteristic and familiar examples. There are all gradations between
the two modes.
Section V. ROOTS.
65. It is a property of stems to produce roots. Stems do not spring from
roots in ordinary cases, as is generally thought, but roots from stems.
When perennial herbs arise from the ground, as they do at spring-time,
they rise from subterranean stems.
66. =The Primary Root= is a downward growth from the root-end of the
caulicle, that is, of the initial stem of the embryo (Fig. 5-7, 81). If
it goes on to grow it makes a _main_ or _tap-root_, as in Fig. 37, etc.
Some plants keep this main root throughout their whole life, and send
off only small side branches; as in the Carrot and Radish: and in
various trees, like the Oak, it takes the lead of the side-branches for
several years, unless accidentally injured, as a strong tap-root. But
commonly the main root divides off very soon, and is lost in the
branches. _Multiple primary roots_ now and then occur, as in the
seedling of Pumpkin (Fig. 27), where a cluster is formed even at the
first, from the root-end of the caulicle.
[Illustration: Fig. 81. Seedling Maple, of the natural size; the root
well supplied with root hairs, here large enough to be seen by the naked
eye. 82. Lower end of this root, magnified, the root seen just as
root-hairs are beginning to form a little behind the tip.]
67. =Secondary Roots= are those which arise from other parts of the
stem. Any part of the stem may produce them, but they most readily come
from the nodes. As a general rule they naturally spring, or may be made
to spring, from almost any young stem, when placed in favorable
circumstances,--that is, when placed in the soil, or otherwise supplied
with moisture and screened from the light. For the special tendency of
the root is to avoid the light, seek moisture, and therefore to bury
itself in the soil. _Propagation by division_, which is so common and so
very important in cultivation, depends upon the proclivity of stems to
strike root. Stems or branches which remain under ground give out roots
as freely as roots themselves give off branches. Stems which creep on
the ground most commonly root at the joints; so will most branches when
bent to the ground, as in propagation by _layering_; and propagation by
_cuttings_ equally depends upon the tendency of the cut end of a shoot
to produce roots. Thus, a piece of a plant which has stem and leaves,
either developed or in the bud, may be made to produce roots, and so
become an independent plant.
68. =Contrast between Stem and Root.= Stems are ascending axes; roots
are descending axes. Stems grow by the successive development of
internodes (13), one after another, each leaf-bearing at its summit (or
node); so that it is of the essential nature of a stem to bear leaves.
Roots bear no leaves, are not distinguishable into nodes and internodes,
but grow on continuously from the lower end. They commonly branch
freely, but not from any fixed points nor in definite order.
69. Although roots generally do not give rise to stems, and therefore do
not propagate the plant, exceptions are not uncommon. For as stems may
produce adventitious buds, so also may roots. The roots of the Sweet
Potato among herbs, and of the Osage Orange among trees freely produce
adventitious buds, developing into leafy shoots; and so these plants are
propagated by _root-cuttings_. But most growths of subterranean origin
which pass for roots are forms of stems, the common Potato for example.
70. Roots of ordinary kinds and uses may be roughly classed into
_fibrous_ and _fleshy_.
71. =Fibrous Roots=, such as those of Indian Corn (Fig. 70), of most
annuals, and of many perennials, serve only for absorption: these are
slender or thread-like. Fine roots of this kind, and the fine branches
which most roots send out are called ROOTLETS.
72. The whole surface of a root absorbs moisture from the soil while
fresh and new; and the newer roots and rootlets are, the more freely do
they imbibe. Accordingly, as long as the plant grows above ground, and
expands fresh foliage, from which moisture largely escapes into the air,
so long it continues to extend and multiply its roots in the soil
beneath, renewing and increasing the fresh surface for absorbing
moisture, in proportion to the demand from above. And when growth ceases
above ground, and the leaves die and fall, or no longer act, then the
roots generally stop growing, and their soft and tender tips harden.
From this period, therefore, until growth begins anew the next spring,
is the best time for transplanting; especially for trees and shrubs.
73. The absorbing surface of young roots is much increased by the
formation, near their tips, of ROOT-HAIRS (Fig. 81, 82), which are
delicate tubular outgrowths from the surface, through the delicate walls
of which moisture is promptly imbibed.
[Illustration: Fig. 83-85. Forms of tap-root.]
74. =Fleshy Roots= are those in which the root becomes a storehouse of
nourishment. Typical roots of this kind are those of such biennials as
the turnip and carrot; in which the food created in the first season's
vegetation is accumulated, to be expended the next season in a vigorous
growth and a rapid development of flowers, fruit, and seed. By the time
the seed is matured the exhausted root dies, and with it the whole
plant.
75. Fleshy roots may be single or multiple. The single root of the
commoner biennials is the primary root, or tap-root, which begins to
thicken in the seedling. Names are given to its shapes, such as
_Conical_, when it thickens most at the crown, or where it joins the
stem, and tapers regularly downwards to a point, as in the Parsnip and
Carrot (Fig. 84);
_Turnip-shaped_ or _napiform_, when greatly thickened above, but
abruptly becoming slender below; as the Turnip (Fig. 83); and
_Spindle-shaped_, or _Fusiform_, when thickest in the middle and
tapering to both ends; as the common Radish (Fig. 85).
76. These examples are of primary roots. It will be seen that turnips,
carrots, and the like, are not pure root throughout; for the caulicle,
from the lower end of which the root grew, partakes of the thickening,
perhaps also some joints of stem above: so the bud-bearing and growing
top is stem.
[Illustration: Fig. 86. Sweet-Potato plant forming thickened roots. Some
in the middle are just beginning to thicken; one at the left has grown
more; one at the right is still larger.]
[Illustration: Fig. 87. Fascicled fusiform roots of a Dahlia: _a_, _a_,
buds on base of stem.]
77. A fine example of secondary roots (67), some of which remain fibrous
for absorption, while a few thicken and store up food for the next
season's growth, is furnished by the Sweet Potato (Fig. 86). As stated
above, these are used for propagation by cuttings; for any part will
produce adventitious buds and shoots. The Dahlia produces _fascicled_
(i. e. clustered) fusiform roots of the same kind, at the base of the
stem (Fig. 87): but these, like most roots, do not produce adventitious
buds. The buds by which Dahlias are propagated belong to the surviving
base of the stem above.
78. =Anomalous Roots=, as they may be called, are those which subserve
other uses than absorption, food-storing, and fixing the plant to the
soil.
_Aerial Roots_, i. e. those that strike from stems in the open air, are
common in moist and warm climates, as in the Mangrove which reaches the
coast of Florida, the Banyan, and, less strikingly, in some herbaceous
plants, such as Sugar Cane, and even in Indian Corn. Such roots reach
the ground at length, or tend to do so.
_Aerial Rootlets_ are abundantly produced by many climbing plants, such
as the Ivy, Poison Ivy, Trumpet Creeper, etc., springing from the side
of stems, which they fasten to trunks of trees, walls, or other
supports. These are used by the plant for climbing.
[Illustration: Fig. 88. Epiphytes of Florida and Georgia, viz.,
Epidendrum conopseum, a small Orchid, and Tillandsia usneoides, the
so-called Long Moss or Black Moss, which is no moss, but a flowering
plant, also _T. recurvata_; on a bough of Live Oak.]
79. =Epiphytes, or Air-Plants= (Fig. 88), are called by the former name
because commonly growing upon the trunks or limbs of other plants; by
the latter because, having no connection with the soil, they must derive
their sustenance from the air only. They have aerial roots, which do not
reach the ground, but are used to fix the plant to the surface upon
which the plant grows: they also take a part in absorbing moisture from
the air.
80. =Parasitic Plants=, of which there are various kinds, strike their
roots, or what answer to roots, into the tissue of foster plants, or
form attachments with their surface, so as to prey upon their juices. Of
this sort is the Mistletoe, the seed of which germinates on the bough
where it falls or is left by birds; and the forming root penetrates the
bark and engrafts itself into the wood, to which it becomes united as
firmly as a natural branch to its parent stem; and indeed the parasite
lives just as if it were a branch of the tree it grows and feeds on. A
most common parasitic herb is the Dodder; which abounds in low grounds
in summer, and coils its long and slender, leafless, yellowish
stems--resembling tangled threads of yarn--round and round the stalks of
other plants; wherever they touch piercing the bark with minute and very
short rootlets in the form of suckers, which draw out the nourishing
juices of the plants laid hold of. Other parasitic plants, like the
Beech-drops and Pine-sap, fasten their roots under ground upon the roots
of neighboring plants, and rob them of their juices.
81. Some plants are partly parasitic; while most of their roots act in
the ordinary way, others make suckers at their tips which grow fast to
the roots of other plants and rob them of nourishment. Some of our
species of Gerardia do this (Fig. 89).
[Illustration: Fig. 89. Roots of Yellow Gerardia, some attached to and
feeding on the root of a Blueberry-bush.]
82. There are phanerogamous plants, like Monotropa or Indian Pipe, the
roots of which feed mainly on decaying vegetable matter in the soil.
These are SAPROPHYTES, and they imitate Mushrooms and other Fungi in
their mode of life.
83. =Duration of Roots, etc.= Roots are said to be either _annual_,
_biennial_, or _perennial_. As respects the first and second, these
terms may be applied either to the root or to the plant.
84. =Annuals=, as the name denotes, live for only one year, generally
for only a part of the year. They are of course herbs; they spring from
the seed, blossom, mature their fruit and seed, and then die, root and
all. Annuals of our temperate climates with severe winters start from
the seed in spring, and perish at or before autumn. Where the winter is
a moist and growing season and the summer is dry, _winter annuals_
prevail; their seeds germinate under autumn or winter rains, grow more
or less during winter, blossom, fructify, and perish in the following
spring or summer. Annuals are fibrous-rooted.
85. =Biennials=, of which the Turnip, Beet, and Carrot are familiar
examples, grow the first season without blossoming, usually thicken
their roots, laying up in them a stock of nourishment, are quiescent
during the winter, but shoot vigorously, blossom, and seed the next
spring or summer, mainly at the expense of the food stored up, and then
die completely. Annuals and biennials flower only once; hence they have
been called _Monocarpic_ (that is, once-fruiting) plants.
86. =Perennials= live and blossom year after year. A perennial herb, in
a temperate or cooler climate, usually dies down to the ground at the
end of the season's growth. But subterranean portions of stem, charged
with buds, survive to renew the development. Shrubs and trees are of
course perennial; even the stems and branches above ground live on and
grow year after year.
87. There are all gradations between annuals and biennials, and between
these and perennials, as also between herbs and shrubs; and the
distinction between shrubs and trees is quite arbitrary. There are
perennial herbs and even shrubs of warm climates which are annuals when
raised in a climate which has a winter,--being destroyed by frost. The
Castor-oil plant is an example. There are perennial herbs of which only
small portions survive, as off-shoots, or, in the Potato, as tubers,
etc.
Section VI. STEMS.
88. =The Stem= is the axis of the plant, the part which bears all the
other organs. Branches are secondary stems, that is, stems growing out
of stems. The stem at the very beginning produces roots, in most plants
a single root from the base of the embryo-stem, or caulicle. As this
root becomes a _descending axis_, so the stem, which grows in the
opposite direction is called the _ascending axis_. Rising out of the
soil, the stem bears leaves; and leaf-bearing is the particular
characteristic of the stem. But there are forms of stems that remain
underground, or make a part of their growth there. These do not bear
leaves, in the common sense; yet they bear rudiments of leaves, or what
answers to leaves, although not in the form of foliage. The so-called
stemless or _acaulescent_ plants are those which bear no obvious stem
(_caulis_) above ground, but only flower-stalks, and the like.
89. =Stems above ground=, through differences in duration, texture, and
size, form herbs, shrubs, trees, etc., or in other terms are
_Herbaceous_, dying down to the ground every year, or after blossoming.
_Suffrutescent_, slightly woody below, there surviving from year to
year.
_Suffruticose_ or _Frutescent_, when low stems are decidedly woody
below, but herbaceous above.
_Fruticose_ or _Shrubby_, woody, living from year to year, and of
considerable size,--not, however, more than three or four times the
height of a man.
_Arborescent_, when tree-like in appearance or mode of growth, or
approaching a tree in size.
_Arboreous_, when forming a proper tree-trunk.
90. As to direction taken in growing, stems may, instead of growing
upright or erect, be
_Diffuse_, that is, loosely spreading in all directions.
_Declined_, when turned or bending over to one side.
_Decumbent_, reclining on the ground, as if too weak to stand.
_Assurgent_ or _Ascending_, rising obliquely upwards.
_Procumbent_ or _Prostrate_, lying flat on the ground from the first.
_Creeping_ or _Repent_, prostrate on or just beneath the ground, and
striking root, as does the White Clover, the Partridge-berry, etc.
_Climbing_ or _Scandent_, ascending by clinging to other objects for
support, whether by _tendrils_, as do the Pea, Grape-Vine, and
Passion-flower and Virginia Creeper (Fig. 92, 93); by their twisting
leaf-stalks, as the Virgin's Bower; or by rootlets, like the Ivy, Poison
Ivy, and Trumpet Creeper.
_Twining_ or _Voluble_, when coiling spirally around other stems or
supports; like the Morning-Glory (Fig. 90) and the Hop.
[Illustration: Fig. 90. Twining or voluble stem of Morning-Glory.]
91. Certain kinds of stems or branches, appropriated to special uses,
have received distinct substantive names; such as the following:
92. =A Culm=, or straw-stem, such as that of Grasses and Sedges.
93. =A Caudex= is the old name for such a peculiar trunk as a Palm-stem;
it is also used for an upright and thick rootstock.
94. =A Sucker= is a branch rising from stems under ground. Such are
produced abundantly by the Rose, Raspberry, and other plants said to
multiply "by the root." If we uncover them, we see at once the great
difference between these subterranean branches and real roots. They are
only creeping branches under ground. Remarking how the upright shoots
from these branches become separate plants, simply by the dying off of
the connecting under-ground stems, the gardener expedites the result by
cutting them through with his spade. That is, he propagates the plant
"by division."
95. =A Stolon= is a branch from above ground, which reclines or becomes
prostrate and strikes root (usually from the nodes) wherever it rests on
the soil. Thence it may send up a vigorous shoot, which has roots of its
own, and becomes an independent plant when the connecting part dies, as
it does after a while. The Currant and the Gooseberry naturally multiply
in this way, as well as by suckers (which are the same thing, only the
connecting part is concealed under ground). Stolons must have suggested
the operation of _layering_ by bending down and covering with soil
branches which do not naturally make stolons; and after they have taken
root, as they almost always will, the gardener cuts through the
connecting stem, and so converts a rooting branch into a separate plant.
96. =An Offset= is a short stolon, or sucker, with a crown of leaves at
the end, as in the Houseleek (Fig. 91), which propagates abundantly in
this way.
[Illustration: Fig. 91. Houseleek (Sempervivum), with offsets.]
97. =A Runner=, of which the Strawberry presents the most familiar and
characteristic example, is a long and slender, tendril-like stolon, or
branch from next the ground, destitute of conspicuous leaves. Each
runner of the Strawberry, after having grown to its full length, strikes
root from the tip, which fixes it to the ground, then forms a bud there,
which develops into a tuft of leaves, and so gives rise to a new plant,
which sends out new runners to act in the same way. In this manner a
single Strawberry plant will spread over a large space, or produce a
great number of plants, in the course of the summer, all connected at
first by the slender runners; but these die in the following winter, if
not before, and leave the plants as so many separate individuals.
98. =Tendrils= are branches of a very slender sort, like runners, not
destined like them for propagation, and therefore always destitute of
buds or leaves, being intended only for climbing. Simple tendrils are
such as those of Passion-flowers (Fig. 92). Compound or branching
tendrils are borne by the Cucumber and Pumpkin, by the Grape-Vine,
Virginia Creeper, etc.
[Illustration: Fig. 92. A small Passion-flower (_Passiflora sicyoides_),
showing the tendrils.]
99. A tendril commonly grows straight and outstretched until it reaches
some neighboring support, such as a stem, when its apex hooks around it
to secure a hold; then the whole tendril shortens itself by coiling up
spirally, and so draws the shoot of the growing plant nearer to the
supporting object. But the tendrils of the Virginia Creeper (Ampelopsis,
Fig. 93), as also the shorter ones of the Japanese species, effect the
object differently, namely, by expanding the tips of the tendrils into a
flat disk, with an adhesive face. This is applied to the supporting
object, and it adheres firmly; then a shortening of the tendril and its
branches by coiling brings up the growing shoot close to the support.
This is an adaptation for climbing mural rocks or walls, or the trunks
of trees, to which ordinary tendrils are unable to cling. The Ivy and
Poison Ivy attain the same result by means of aerial rootlets (78).
[Illustration: Fig. 93. Piece of the stem of Virginia Creeper, bearing a
leaf and a tendril. 94. Tips of a tendril, about the natural size,
showing the disks by which they hold fast to walls, etc.]
100. Some tendrils are leaves or parts of leaves, as those of the Pea
(Fig. 35). The nature of the tendril is known by its position. A tendril
from the axil of a leaf, like that of Passion-flowers (Fig. 92) is of
course a stem, i. e. a branch. So is one which terminates a stem, as in
the Grape-Vine.
101. =Spines= or =Thorns= (Fig. 95, 96) are commonly stunted and
hardened branches or tips of stems or branches, as are those of
Hawthorn, Honey-Locust, etc. In the Pear and Sloe all gradations occur
between spines and spine-like (spinescent) branches. Spines may be
reduced and indurated leaves; as in the Barberry, where their nature is
revealed by their situation, underneath an axillary bud. But prickles,
such as those of Blackberry and Roses, are only excrescences of the
bark, and not branches.
[Illustration: Fig. 95. A branching thorn of Honey-Locust, being an
indurated leafless branch developed from an accessory bud far above the
axil: at the cut portion below, three other buds (_a_) are concealed
under the petiole.]
[Illustration: Fig. 96. Spine of Cockspur Thorn, developed from an
axillary bud, as the leaf-scar below witnesses: an accessory leaf-bud is
seen at its base.]
102. Equally strange forms of stems are characteristic of the Cactus
family (Fig. 111). These may be better understood by comparison with
103. =Subterranean Stems and Branches.= These are very numerous and
various; but they are commonly overlooked, or else are confounded with
roots. From their situation they are out of ordinary sight; but they
will well repay examination. For the vegetation that is carried on under
ground is hardly less varied or important than that above ground. All
their forms may be referred to four principal kinds: namely, the
_Rhizoma_ (_Rhizome_) or _Rootstock_, the _Tuber_, the _Corm_ or solid
bulb, and the true _Bulb_.
[Illustration: Fig. 97. Rootstocks, or creeping subterranean branches,
of the Peppermint.]
104. =The Rootstock, or Rhizoma=, in its simplest form, is merely a
creeping stem or branch growing beneath the surface of the soil, or
partly covered by it. Of this kind are the so-called _creeping_,
_running_, or _scaly roots_, such as those by which the Mint (Fig. 97),
the Couch-grass, or Quick-grass, and many other plants, spread so
rapidly and widely,--"by the root," as it is said. That these are really
_stems_, and not roots, is evident from the way in which they grow;
from their consisting of a succession of joints; and from the leaves
which they bear on each _node_, in the form of small scales, just like
the lowest ones on the upright stem next the ground. They also produce
buds in the axils of these scales, showing the scales to be leaves;
whereas real roots bear neither leaves nor axillary buds. Placed as they
are in the damp and dark soil, such stems naturally produce roots, just
as the creeping stem does where it lies on the surface of the ground.
105. It is easy to see why plants with these running rootstocks take
such rapid and wide possession of the soil, and why they are so hard to
get rid of. They are always perennials; the subterranean shoots live
over the first winter, if not longer, and are provided with vigorous
buds at every joint. Some of these buds grow in spring into upright
stems, bearing foliage, to elaborate nourishment, and at length produce
blossoms for reproduction by seed; while many others, fed by nourishment
supplied from above, form a new generation of subterranean shoots; and
this is repeated over and over in the course of the season or in
succeeding years. Meanwhile, as the subterranean shoots increase in
number, the older ones, connecting the successive growths, die off year
by year, liberating the already rooted side-branches as so many separate
plants; and so on indefinitely. Cutting these running rootstocks into
pieces, therefore, by the hoe or the plough, far from destroying the
plant, only accelerates the propagation; it converts one many-branched
plant into a great number of separate individuals. Cutting into pieces
only multiplies the pest; for each piece (Fig. 98) is already a
plantlet, with its roots and with a bud in the axil of its scale-like
leaf (either latent or apparent), and with prepared nourishment enough
to develop this bud into a leafy stem; and so a single plant is all the
more speedily converted into a multitude. Whereas, when the subterranean
parts are only roots, cutting away the stem completely destroys the
plant, except in the rather rare cases where the root freely produces
adventitious buds.
[Illustration: Fig. 98. A piece of the running rootstock of the
Peppermint, with its node or joint, and an axillary bud ready to grow.]
106. Rootstocks are more commonly thickened by the storing up of
considerable nourishing matter in their tissue. The common species of
Iris (Fig. 164) in the gardens have stout rootstocks, which are only
partly covered by the soil, and which bear foliage-leaves instead of
mere scales, closely covering the upper part, while the lower produces
roots. As the leaves die, year by year, and decay, a scar left in the
form of a ring marks the place where each leaf was attached, that is,
marks so many nodes, separated by very short internodes.
107. Some rootstocks are marked with large round scars of a different
sort, like those of the Solomon's Seal (Fig. 99), which gave this name
to the plant, from their looking somewhat like the impression of a seal
upon wax. Here the rootstock sends up every spring an herbaceous stalk
or stem, which bears the foliage and flowers, and dies in autumn. The
_seal_ is the circular scar left by the death and separation of the base
of the stout stalk from the living rootstock. As but one of these is
formed each year, they mark the limits of a year's growth. The bud at
the end of the rootstock in the figure (which was taken in summer) will
grow the next spring into the stalk of the season, which, dying in
autumn, will leave a similar scar, while another bud will be formed
farther on, crowning the ever-advancing summit or growing end of the
stem.
[Illustration: Fig. 99. Rootstock of Solomon's Seal, with the bottom of
the stalk of the season, and the bud for the next year's growth.]
108. As each year's growth of stem makes its own roots, it soon becomes
independent of the older parts. And after a certain age, a portion
annually dies off behind, about as fast as it increases at the growing
end, death following life with equal and certain step, with only a
narrow interval. In vigorous plants of Solomon's Seal or Iris, the
living rootstock is several inches or a foot in length; while in the
short rootstock of Trillium or Birthroot (Fig. 100) life is reduced to a
narrower span.
[Illustration: Fig. 100. The very short rootstock and strong terminal
bud of a Trillium or Birthroot.]
109. An upright or short rootstock, like this of Trillium, is commonly
called a CAUDEX (93); or when more shortened and thickened it would
become a corm.
110. =A Tuber= may be understood to be a portion of a rootstock
thickened, and with buds (eyes) on the sides. Of course, there are all
gradations between a tuber and a rootstock. Helianthus tuberosus, the
so-called Jerusalem Artichoke (Fig. 101), and the common Potato, are
typical and familiar examples of the tuber. The stalks by which the
tubers are attached to the parent stem are at once seen to be different
from the roots, both in appearance and manner of growth. The scales on
the tubers are the rudiments of leaves; the eyes are the buds in their
axils. The Potato-plant has three forms of branches: 1. Those that bear
ordinary leaves expanded in the air, to digest what they gather from it
and what the roots gather from the soil, and convert it into
nourishment. 2. After a while a second set of branches at the summit of
the plant bear flowers, which form fruit and seed out of a portion of
the nourishment which the leaves have prepared. 3. But a larger part of
this nourishment, while in a liquid state, is carried down the stem,
into a third sort of branches under ground, and accumulated in the form
of starch at their extremities, which become tubers, or depositories of
prepared solid food,--just as in the Turnip, Carrot, and Dahlia (Fig.
83-87), it is deposited in the root. The use of the store of food is
obvious enough. In the autumn the whole plant dies, except the seeds (if
it formed them) and the tubers; and the latter are left disconnected in
the ground. Just as that small portion of nourishing matter which is
deposited in the seed feeds the embryo when it germinates, so the much
larger portion deposited in the tuber nourishes its buds, or eyes, when
they likewise grow, the next spring, into new plants. And the great
supply enables them to shoot with a greater vigor at the beginning, and
to produce a greater amount of vegetation than the seedling plant could
do in the same space of time; which vegetation in turn may prepare and
store up, in the course of a few weeks or months, the largest quantity
of solid nourishing material, in a form most available for food. Taking
advantage of this, man has transported the Potato from the cool Andes of
Chili to other cool climates, and makes it yield him a copious supply of
food, especially important in countries where the season is too short,
or the summer's heat too little, for profitably cultivating the
principal grain-plants.
[Illustration: Fig. 101. Tubers of Helianthus tuberosus, called
"artichokes."]
[Illustration: Fig. 102. Bulblet-like tubers, such as are occasionally
formed on the stem of a Potato-plant above ground.]
111. =The Corm or Solid Bulb=, like that of Cyclamen (Fig. 103), and of
Indian Turnip (Fig. 104), is a very short and thick fleshy subterranean
stem, often broader than high. It sends off roots from its lower end, or
rather face, leaves and stalks from its upper. The corm of Cyclamen goes
on to enlarge and to produce a succession of flowers and leaves year
after year. That of Indian Turnip is formed one year and is consumed
the next. Fig. 104 represents it in early summer, having below the corm
of last year, from which the roots have fallen. It is partly consumed by
the growth of the stem for the season, and the corm of the year is
forming at base of the stem above the line of roots.
[Illustration: Fig. 103. Corm of Cyclamen, much reduced in size: roots
from lower face, leaf-stalks and flower-stalks from the upper.]
[Illustration: Fig. 104. Corm of Indian Turnip (Arisaema).]
112. The corm of Crocus (Fig. 105, 106), like that of its relative
Gladiolus, is also reproduced annually, the new ones forming upon the
summit and sides of the old. Such a corm is like a tuber in budding from
the sides, i. e. from the axils of leaves; but these leaves, instead of
being small scales, are the sheathing bases of foliage-leaves which
covered the surface. It resembles a true bulb in having these sheaths or
broad scales; but in the corm or solid bulb, this solid part or stem
makes up the principal bulk.
[Illustration: Fig. 105. Corm of a Crocus, the investing sheaths or dead
leaf-bases stripped off. The faint cross-lines represent the scars,
where the leaves were attached, i. e. the nodes: the spaces between are
the internodes. The exhausted corm of the previous year is underneath;
forming ones for next year on the summit and sides.]
[Illustration: Fig. 106. Section of the same.]
113. =The Bulb=, strictly so-called, is a stem like a reduced corm as to
its solid part (or plate); while the main body consists of thickened
scales, which are leaves or leaf-bases. These are like bud-scales; so
that in fact a bulb is a bud with fleshy scales on an exceedingly short
stem. Compare a White Lily bulb (Fig. 107) with the strong scaly buds of
the Hickory and Horse-chestnut (Fig. 72 and 73), and the resemblance
will appear. In corms, as in tubers and rootstocks, the store of food
for future growth is deposited in the stem; while in the bulb, the
greater part is deposited in the bases of the leaves, changing them into
thick scales, which closely overlap or enclose one another.
114. =A Scaly Bulb= (like that of the Lily, Fig. 107, 108) is one in
which the scales are thick but comparatively narrow.
[Illustration: Fig. 107. Bulb of a wild Lily. 108. The same divided
lengthwise, showing two forming buds of the next generation.]
[Illustration: Fig. 109. A ground leaf of White Lily, its base (cut
across) thickened into a bulb-scale. This plainly shows that bulb-scales
are leaves.]
115. =A Tunicated or Coated Bulb= is one in which the scales enwrap each
other, forming concentric coats or layers, as in Hyacinth and Onion.
116. =Bulblets= are very small bulbs growing out of larger ones; or
small bulbs produced above ground on some plants, as in the axils of the
leaves of the bulbiferous Lilies of the gardens (Fig. 110), and often in
the flower-clusters of the Leek and Onion. They are plainly buds with
thickened scales. They never grow into branches, but detach themselves
when full grown, fall to the ground, and take root there to form new
plants.
[Illustration: Fig. 110. Bulblets in the axils of leaves of a Tiger
Lily.]
117. =Consolidated Vegetation.= An ordinary herb, shrub, or tree is
evidently constructed on the plan developing an extensive surface. In
fleshy rootstocks, tubers, corms, and bulbs, the more enduring portion
of the plant is concentrated, and reduced for the time of struggle (as
against drought, heat, or cold) to a small amount of exposed surface,
and this mostly sheltered in the soil. There are many similar
consolidated forms which are not subterranean. Thus plants like the
Houseleek (Fig. 91) imitate a bulb. Among Cactuses the columnar species
of Cereus (Fig. 111, _b_), may be likened to rootstocks. A green rind
serves the purpose of foliage; but the surface is as nothing compared
with an ordinary leafy plant of the same bulk. Compare, for instance,
the largest Cactus known, the Giant Cereus of the Gila River (Fig. 111,
in the background), which rises to the height of fifty or sixty feet,
with a common leafy tree of the same height, such as that in Fig. 89,
and estimate how vastly greater, even without the foliage, the surface
of the latter is than that of the former. Compare, in the same view, an
Opuntia or Prickly-Pear Cactus, its stem and branches formed of a
succession of thick and flattened joints (Fig. 111, _a_), which may be
likened to tubers, or an Epiphyllum (_d_), having short and flat joints,
with an ordinary leafy shrub or herb of equal size. And finally, in
Melon-Cactuses, Echinocactus (_c_), or other globose forms (which may be
likened to permanent corms), with their globular or bulb-like shapes, we
have plants in the compactest shape; their spherical figure being such
as to expose the least possible amount of substance to the air. These
are adaptations to climates which are very dry, either throughout or for
a part of the year. Similarly, bulbous and corm-bearing plants, and the
like, are examples of a form of vegetation which in the growing season
may expand a large surface to the air and light, while during the period
of rest the living vegetable is reduced to a globe, or solid form of the
least possible surface; and this protected by its outer coats of dead
and dry scales, as well as by its situation under ground. Such are also
adapted to a season of drought. They largely belong to countries which
have a long hot season of little or no rain, when, their stalks and
foliage above and their roots beneath early perishing, the plants rest
securely in their compact bulbs, filled with nourishment and retaining
their moisture with great tenacity, until the rainy season comes round.
Then they shoot forth leaves and flowers with wonderful rapidity, and
what was perhaps a desert of arid sand becomes green with foliage and
gay with blossoms, almost in a day.
[Illustration: Fig. 111.]
Section VII. LEAVES.
118. STEMS bear leaves, at definite points (nodes, 13); and these are
produced in a great variety of forms, and subserve various uses. The
commonest kind of leaf, which therefore may be taken as the type or
pattern, is an expanded green body, by means of which the plant exposes
to the air and light the matters which it imbibes, exhales certain
portions, and assimilates the residue into vegetable matter for its
nourishment and growth.
119. But the fact is already familiar (10-30) that leaves occur under
other forms and serve for other uses,--for the storage of food already
assimilated, as in thickened seed-leaves and bulb-scales; for covering,
as in bud-scales; and still other uses are to be pointed out. Indeed,
sometimes they are of no service to the plant, being reduced to mere
scales or rudiments, such as those on the rootstocks of Peppermint (Fig.
97) or the tubers of Jerusalem Artichoke (Fig. 101). These may be said
to be of service only to the botanist, in explaining to him the plan
upon which a plant is constructed.
120. Accordingly, just as a rootstock, or a tuber, or a tendril is a
kind of stem, so a bud-scale, or a bulb-scale, or a cotyledon, or a
petal of a flower, is a kind of leaf. Even in respect to ordinary
leaves, it is natural to use the word either in a wider or in a narrower
sense; as when in one sense we say that a leaf consists of blade and
petiole or leaf-stalk, and in another sense say that a leaf is petioled,
or that the leaf of Hepatica is three-lobed. The connection should make
it plain whether by leaf we mean leaf-blade only, or the blade with any
other parts it may have. And the student will readily understand that by
leaf in its largest or _morphological_ sense, the botanist means the
organ which occupies the place of a leaf, whatever be its form or its
function.
Sec. 1. LEAVES AS FOLIAGE.
121. This is tautological; for foliage is simply leaves: but it is very
convenient to speak of typical leaves, or those which serve the plant
for assimilation, as foliage-leaves, or ordinary leaves. These may first
be considered.
122. =The Parts of a Leaf.= The ordinary leaf, complete in its parts,
consists of _blade_, _foot-stalk_, or _petiole_, and a pair of
_stipules_.
123. First the BLADE or LAMINA, which is the essential part of ordinary
leaves, that is, of such as serve the purpose of foliage. In structure
it consists of a softer part, the _green pulp_, called _parenchyma_,
which is traversed and supported by a fibrous frame, the parts of which
are called _ribs_ or _veins_, on account of a certain likeness in
arrangement to the veins of animals. The whole surface is covered by a
transparent skin, the _Epidermis_, not unlike that which covers the
surface of all fresh shoots.
124. Note that the leaf-blade expands horizontally,--that is, normally
presents its faces one to the sky, the other to the ground, or when the
leaf is erect the upper face looks toward the stem that bears it, the
lower face away from it. Whenever this is not the case there is
something to be explained.
125. The framework consists of _wood_,--a fibrous and tough material
which runs from the stem through the leaf-stalk, when there is one, in
the form of parallel threads or bundles of fibres; and in the blade
these spread out in a horizontal direction, to form the _ribs_ and
_veins_ of the leaf. The stout main branches of the framework are called
the _Ribs_. When there is only one, as in Fig. 112, 114, or a middle one
decidedly larger than the rest, it is called the _Midrib_. The smaller
divisions are termed _Veins_; and their still smaller subdivisions,
_Veinlets_. The latter subdivide again and again, until they become so
fine that they are invisible to the naked eye. The fibres of which they
are composed are hollow; forming tubes by which the sap is brought into
the leaves and carried to every part.
[Illustration: Fig. 112. Leaf of the Quince: _b_, blade; _p_, petiole;
_st_, stipules.]
126. =Venation= is the name of the mode of veining, that is, of the way
in which the veins are distributed in the blade. This is of two
principal kinds; namely, the _parallel-veined_, and the _netted-veined_.
127. In _Netted-veined_ (also called _Reticulated_) leaves, the veins
branch off from the main rib or ribs, divide into finer and finer
veinlets, and the branches unite with each other to form meshes of
network. That is, they _anastomose_, as anatomists say of the veins and
arteries of the body. The Quince-leaf, in Fig. 112, shows this kind of
veining in a leaf with a single rib. The Maple, Basswood, Plane or
Buttonwood (Fig. 74) show it in leaves of several ribs.
128. In _parallel-veined_ leaves, the whole framework consists of
slender ribs or veins, which run parallel with each other, or nearly so,
from the base to the point of the leaf,--not dividing and subdividing,
nor forming meshes, except by minute cross-veinlets. The leaf of any
grass, or that of the Lily of the Valley (Fig. 113) will furnish a good
illustration. Such parallel veins Linnaeus called _Nerves_, and
parallel-veined leaves are still commonly called _nerved_ leaves, while
those of the other kind are said to be _veined_,--terms which it is
convenient to use, although these "nerves" and "veins" are all the same
thing, and have no likeness to the _nerves_ and little to the veins of
animals.
129. _Netted-veined_ leaves belong to plants which have a pair of
seed-leaves or cotyledons, such as the Maple (Fig. 20, 24), Beech (Fig.
33), and the like; while _parallel-veined_ or _nerved_ leaves belong to
plants with one cotyledon or true seed-leaf; such as the Iris (Fig. 59),
and Indian Corn (Fig. 70). So that a mere glance at the leaves generally
tells what the structure of the embryo is, and refers the plant to one
or the other of these two grand classes,--which is a great convenience.
For when plants differ from each other in some one important respect,
they usually differ correspondingly in other respects also.
[Illustration: Fig. 113. A (parallel-veined) leaf of the Lily of the
Valley. 114. One of the Calla Lily.]
130. Parallel-veined leaves are of two sorts,--one kind, and the
commonest, having the ribs or nerves all running from the base to the
point of the leaf, as in the examples already given; while in another
kind they run from a midrib to the margin, as in the common
Pickerel-weed of our ponds, in the Banana, in Calla (Fig. 114), and many
similar plants of warm climates.
131. Netted-veined leaves are also of two sorts, as in the examples
already referred to. In one case the veins all rise from a single rib
(the midrib), as in Fig. 112, 116-127. Such leaves are called
_Feather-veined_ or _Penni-veined_, i. e. _Pinnately-veined_; both terms
meaning the same thing, namely, that the veins are arranged on the sides
of the rib like the plume of a feather on each side of the shaft.
132. In the other case (as in Fig. 74, 129-132), the veins branch off
from three, five, seven, or nine ribs, which spread from the top of the
leaf-stalk, and run through the blade like the toes of a web-footed
bird. Hence these are said to be _Palmately_ or _Digitately_ veined, or
(since the ribs diverge like rays from a centre) _Radiate-veined_.
133. Since the general outline of leaves accords with the framework or
skeleton, it is plain that _feather-veined_ (or _penni-veined_) leaves
will incline to elongated shapes, or at least to be longer than broad;
while in _radiate-veined_ leaves more rounded forms are to be expected.
A glance at the following figures shows this.
[Illustration: Fig. 115-120. A series of shapes of feather-veined
leaves.]
134. =Forms of Leaves as to General Outline.= It is necessary to give
names to the principal shapes, and to define them rather precisely,
since they afford easy marks for distinguishing species. The same terms
are used for all other flattened parts as well, such as petals; so that
they make up a great part of the descriptive language of Botany. It will
be a good exercise for young students to look up leaves answering to
these names and definitions. Beginning with the narrower and proceeding
to the broadest forms, a leaf is said to be
_Linear_ (Fig. 115), when narrow, several times longer than wide, and of
the same breadth throughout.
_Lanceolate_, or _Lance-shaped_, when conspicuously longer than wide,
and tapering upwards (Fig. 116), or both upwards and downwards.
_Oblong_ (Fig. 117), when nearly twice or thrice as long as broad.
_Elliptical_ (Fig. 118) is oblong with a flowing outline, the two ends
alike in width.
_Oval_ is the same as broadly elliptical, or elliptical with the breadth
considerably more than half the length.
_Ovate_ (Fig. 119), when the outline is like a section of a hen's egg
lengthwise, the broader end downward.
_Orbicular_, or _Rotund_ (Fig. 132), circular in outline, or nearly so.
[Illustration: Fig. 121, oblanceolate; 122, spatulate; 123, obovate; and
124, wedge-shaped, feather-veined, leaves.]
135. A leaf which tapers toward the base instead of toward the apex may
be
_Oblanceolate_ (Fig. 121) when of the lance-shaped form, only more
tapering toward the base than in the opposite direction.
_Spatulate_ (Fig. 122) when more rounded above, but tapering thence to a
narrow base, like an old-fashioned spatula.
_Obovate_ (Fig. 123) or inversely ovate, that is, ovate with the
narrower end down.
_Cuneate_ or _Cuneiform_, that is, _Wedge-shaped_ (Fig. 124), broad
above and tapering by nearly straight lines to an acute angle at the
base.
[Illustration: Fig. 125, sagittate; 126, auriculate; and 127,
halberd-shaped or hastate leaves.]
136. =As to the Base=, its shape characterizes several forms, such as
_Cordate_ or _Heart-shaped_ (Fig. 120, 129), when a leaf of an ovate
form, or something like it, has the outline of its rounded base turned
in (forming a notch or _sinus_) where the stalk is attached.
_Reniform_, or _Kidney-shaped_ (Fig. 131), like the last, only rounder
and broader than long.
_Auriculate_, or _Eared_, having a pair of small and blunt projections,
or _ears_, at the base, as in one species of Magnolia (Fig. 126).
_Sagittate_, or _arrow-shaped_, where such ears are acute and turned
downwards, while the main body of the blade tapers upwards to a point,
as in the common Sagittaria or Arrow-head, and in the Arrow-leaved
Polygonum (Fig. 125).
_Hastate_, or _Halberd-shaped_, when such lobes at the base point
outwards, giving the shape of the halberd of the olden time, as in
another Polygonum (Fig. 127).
[Illustration: Fig. 128-132. Various forms of radiate-veined leaves.]
_Peltate_, or _Shield-shaped_ (Fig. 132), is the name applied to a
curious modification of the leaf, commonly of a rounded form, where the
footstalk is attached to the lower surface, instead of the base, and
therefore is naturally likened to a shield borne by the outstretched
arm. The common Watershield, the Nelumbium, and the White Water-lily,
and also the Mandrake, exhibit this sort of leaf. On comparing the
shield-shaped leaf of the common Marsh Pennywort (Fig. 132) with that of
another common species (Fig. 130), it is at once seen that a
shield-shaped leaf is like a kidney-shaped (Fig. 130, 131) or other
rounded leaf, with the margins at the base brought together and united.
137. =As to the Apex=, the following terms express the principal
variations:--
_Acuminate_, _Pointed_, or _Taper-pointed_, when the summit is more or
less prolonged into a narrowed or tapering point; as in Fig. 133.
_Acute_, ending in an acute angle or not prolonged point; Fig. 134.
_Obtuse_, with a blunt or rounded apex; as in Fig. 135, etc.
_Truncate_, with the end as if cut off square; as in Fig. 136.
_Retuse_, with rounded summit slightly indented, forming a very shallow
notch, as in Fig. 137.
_Emarginate_, or _Notched_, indented at the end more decidedly; as in
Fig. 138.
_Obcordate_, that is, inversely heart-shaped, where an obovate leaf is
more deeply notched at the end (Fig. 139), as in White Clover and
Wood-sorrel; so as to resemble a cordate leaf inverted.
_Cuspidate_, tipped with a sharp and rigid point; as in Fig. 140.
_Mucronate_, abruptly tipped with a small and short point, like a mere
projection of the midrib; as in Fig. 141.
_Aristate_, _Awn-pointed_, and _Bristle-pointed_, are terms used when
this mucronate point is extended into a longer bristle-form or slender
appendage.
The first six of these terms can be applied to the lower as well as to
the upper end of a leaf or other organ. The others belong to the apex
only.
[Illustration: Fig. 133-141. Forms of the apex of leaves.]
138. =As to degree and nature of Division=, there is first of all the
difference between
_Simple Leaves_, those in which the blade is of one piece, however much
it may be cut up, and
_Compound Leaves_, those in which the blade consists of two or more
separate pieces, upon a common leaf-stalk or support. Yet between these
two kinds every intermediate gradation is to be met with.
[Illustration: Fig. 142-147. Kinds of margin of leaves.]
139. =As to Particular Outlines of Simple Leaves= (and the same applies
to their separate parts), they are
_Entire_, when their general outline is completely filled out, so that
the margin is an even line, without teeth or notches.
_Serrate_, or _Saw-toothed_, when the margin only is cut into sharp
teeth, like those of a saw, and pointing forwards; as in Fig. 142.
_Dentate_, or _Toothed_, when such teeth point outwards, instead of
forwards; as in Fig. 143.
_Crenate_, or _Scalloped_, when the teeth are broad and rounded; as in
Fig. 144.
_Repand_, _Undulate_, or _Wavy_, when the margin of the leaf forms a
wavy line, bending slightly inwards and outwards in succession; as in
Fig. 145.
_Sinuate_, when the margin is more strongly sinuous or turned inwards
and outwards; as in Fig. 146.
_Incised_, _Cut_, or _Jagged_, when the margin is cut into sharp, deep,
and irregular teeth or incisions; as in Fig. 147.
_Lobed_, when deeply cut. Then the pieces are in a general way called
LOBES. The number of the lobes is briefly expressed by the phrase
_two-lobed_, _three-lobed_, _five-lobed_, _many-lobed_, etc., as the
case may be.
140. When the depth and character of the lobing needs to be more
particularly specified, the following terms are employed, viz.:--
_Lobed_, in a special sense, when the incisions do not extend deeper
than about half-way between the margin and the centre of the blade, if
so far, and are more or less rounded; as in the leaves of the Post-Oak,
Fig. 148, and the Hepatica, Fig. 152.
_Cleft_, when the incisions extend half way down or more, and especially
when they are sharp; as in Fig. 149, 153. And the phrases _two-cleft_,
or, in the Latin form, _bifid_, _three-cleft_ or _trifid_, _four-cleft_
or _quadrifid_, _five-cleft_ or _quinquefid_, etc., or _many-cleft_, in
the Latin form, _multifid_,--express the number of the _Segments_, or
portions.
_Parted_, when the incisions are still deeper, but yet do not quite
reach to the midrib or the base of the blade; as in Fig. 150, 154. And
the terms _two-parted_, _three-parted_, etc., express the number of such
divisions.
_Divided_, when the incisions extend quite to the midrib, as in the
lower part of Fig. 151, or to the leaf-stalk, as in Fig. 155; which
really makes the leaf compound. Here, using the Latin form, the leaf is
said to be _bisected_, _trisected_ (Fig. 155), etc., according to the
number of the divisions.
[Illustration: Fig. 148, pinnately lobed; 149, pinnately cleft; 150,
pinnately parted; 151, pinnately divided, leaves.]
[Illustration: Fig. 152, palmately three-lobed; 153, palmately
three-cleft; 154, palmately three-parted; 155, palmately three-divided
or trisected, leaves.]
141. =The Mode of Lobing or Division= corresponds to that of the
veining, whether _pinnately veined_ or _palmately veined_. In the former
the notches or incisions, or _sinuses_, coming between the principal
veins or ribs are directed toward the midrib: in the latter they are
directed toward the apex of the petiole; as the figures show.
142. So degree and mode of division may be tersely expressed in brief
phrases. Thus, in the four upper figures of pinnately veined leaves, the
first is said to be _pinnately lobed_ (in the special sense), the second
_pinnately cleft_ (or _pinnatifid_ in Latin form), the third _pinnately
parted_, the fourth _pinnately divided_, or _pinnatisected_.
143. Correspondingly in the lower row, of palmately veined leaves, the
first is _palmately lobed_, the second _palmately cleft_, the third
_palmately parted_, the fourth _palmately divided_. Or, in other
language of the same meaning (but now less commonly employed), they are
said to be _digitately lobed_, _cleft_, _parted_, or _divided_.
144. The number of the divisions or lobes may come into the phrase. Thus
in the four last named figures the leaves are respectively _palmately
three-lobed_, _three-cleft_ (or _trifid_), _three-parted_,
_three-divided_, or better (in Latin form), _trisected_. And so for
higher numbers, as _five-lobed_, _five-cleft_, etc., up to
_many-lobed_, _many-cleft_ or _multifid_, etc. The same mode of
expression may be used for pinnately lobed leaves, as _pinnately
7-lobed_, _-cleft_, _-parted_, etc.
145. The divisions, lobes, etc., may themselves be _entire_ (without
teeth or notches), or _serrate_, or otherwise toothed or incised; or
lobed, cleft, parted, etc.: in the latter cases making _twice
pinnatifid_, _twice palmately_ or _pinnately lobed_, _parted_, or
_divided_ leaves, etc. From these illustrations one will perceive how
the botanist, in two or three words, may describe any one of the almost
endlessly diversified shapes of leaves, so as to give a clear and
definite idea of it.
146. =Compound Leaves.= A compound leaf is one which has its blade in
entirely separate parts, each usually with a stalklet of its own; and
the stalklet is often _jointed_ (or _articulated_) with the main
leaf-stalk, just as this is jointed with the stem. When this is the
case, there is no doubt that the leaf is compound. But when the pieces
have no stalklets, and are not jointed with the main leaf-stalk, it may
be considered either as a divided simple leaf, or a compound leaf,
according to the circumstances. This is a matter of names where all
intermediate forms may be expected.
147. While the pieces or projecting parts of a simple leaf-blade are
called _Lobes_, or in deeply cut leaves, etc., _Segments_, or
_Divisions_, the separate pieces or blades of a compound leaf are called
LEAFLETS.
148. Compound leaves are of two principal kinds, namely, the _Pinnate_
and the _Palmate_; answering to the two modes of veining in reticulated
leaves, and to the two sorts of lobed or divided leaves (141).
[Illustration: Fig. 156-158. Pinnate leaves, the first with an odd
leaflet (_odd-pinnate_); the second with a tendril in place of uppermost
leaflets; the third _abruptly pinnate_, or of even pairs.]
149. _Pinnate_ leaves are those in which the leaflets are arranged on
the sides of a main leaf-stalk; as in Fig. 156-158. They answer to the
_feather-veined_ (i. e. _pinnately-veined_) simple leaf; as will be
seen at once on comparing the forms. The _leaflets_ of the former answer
to the _lobes_ or _divisions_ of the latter; and the continuation of the
petiole, along which the leaflets are arranged, answers to the midrib of
the simple leaf.
150. Three sorts of pinnate leaves are here given. Fig. 156 is _pinnate
with an odd_ or _end leaflet_, as in the Common Locust and the Ash. Fig.
157 is _pinnate with a tendril at the end_, in place of the odd leaflet,
as in the Vetches and the Pea. Fig. 158 is evenly or _abruptly pinnate_,
as in the Honey-Locust.
[Illustration: Fig. 159. Palmate (or digitate) leaf of five leaflets, of
the Sweet Buckeye.]
151. _Palmate_ (also named _Digitate_) leaves are those in which the
leaflets are all borne on the tip of the leaf-stalk, as in the Lupine,
the Common Clover, the Virginia Creeper (Fig. 93), and the
Horse-chestnut and Buckeye (Fig. 159). They evidently answer to the
_radiate-veined_ or _palmately-veined_ simple leaf. That is, the
Clover-leaf of three leaflets is the same as a palmately three-ribbed
leaf cut into three separate leaflets. And such a simple five-lobed leaf
as that of the Sugar Maple, if more cut, so as to separate the parts,
would produce a palmate leaf of five leaflets, like that of the
Horse-chestnut or Buckeye.
152. Either sort of compound leaf may have any number of leaflets; yet
palmate leaves cannot well have a great many, since they are all crowded
together on the end of the main leaf-stalk. Some Lupines have nine or
eleven; the Horse-chestnut has seven, the Sweet Buckeye more commonly
five, the Clover three. A pinnate leaf often has only seven or five
leaflets, or only three, as in Beans of the genus Phaseolus, etc.; in
some rarer cases only two; in the Orange and Lemon and also in the
common Barberry there is only one! The joint at the place where the
leaflet is united with the petiole distinguishes this last case from a
simple leaf. In other species of these genera the lateral leaflets also
are present.
153. The leaflets of a compound leaf may be either _entire_ (as in Fig.
126-128), or _serrate_, or lobed, cleft, parted, etc.; in fact, may
present all the variations of simple leaves, and the same terms equally
apply to them.
154. When the division is carried so far as to separate what would be
one leaflet into two, three, or several, the leaf becomes _doubly_ or
_twice compound_, either _pinnately_ or _palmately_, as the case may be.
For example, while the clustered leaves of the Honey-Locust are _simply
pinnate_, that is, _once pinnate_, those on new shoots are _bipinnate_,
or _twice pinnate_, as in Fig. 160. When these leaflets are again
divided in the same way, the leaf becomes _thrice pinnate_, or
_tripinnate_, as in many Acacias. The first divisions are called
_Pinnae_; the others, _Pinnules_; and the last, or little blades
themselves, _Leaflets_.
[Illustration: Fig. 160. A twice-pinnate (abruptly) leaf of the
Honey-Locust.]
155. So the palmate leaf, if again compounded in the same way, becomes
_twice palmate_, or, as we say when the divisions are in threes, _twice
ternate_ (in Latin form _biternate_); if a third time compounded,
_thrice ternate_ or _triternate_. But if the division goes still
further, or if the degree is variable, we simply say that the leaf is
_decompound_; either palmately or pinnately decompound, as the case may
be. Thus, Fig. 161 represents a four times ternately compound (in other
words a _ternately decompound_) leaf of a common Meadow Rue.
[Illustration: Fig. 161. Ternately decompound leaf of Meadow Rue.]
156. When the botanist, in describing leaves, wishes to express the
number of the leaflets, he may use terms like these:--
_Unifoliolate_, for a compound leaf of a single leaflet; from the Latin
_unum_, one, and _foliolum_, leaflet.
_Bifoliolate_, of two leaflets, from the Latin _bis_, twice, and
_foliolum_, leaflet.
_Trifoliolate_ (or _ternate_), of three leaflets, as the Clover; and so
on.
_Palmately bifoliolate_, _trifoliolate_, _quadrifoliolate_,
_plurifoliolate_ (of several leaflets), etc.: or else
_Pinnately bi-_, _tri-_, _quadri-_, or _plurifoliolate_ (that is, of
two, three, four, five, or several leaflets), as the case may be: these
are terse ways of denoting in single phrases both the number of leaflets
and the kind of compounding.
157. Of foliage-leaves having certain peculiarities in structure, the
following may be noted:--
158. =Perfoliate Leaves.= In these the stem that bears them seems to
run through the blade of the leaf, more or less above its base. A common
Bellwort (Uvularia perfoliata, Fig. 162) is a familiar illustration. The
lower and earlier leaves show it distinctly. Later, the plant is apt to
produce some leaves merely clasping the stem by the sessile and
heart-shaped base, and the latest may be merely sessile. So the series
explains the peculiarity: in the formation of the leaf the bases,
meeting around the stem, grow together there.
[Illustration: Fig. 162. A summer branch of Uvularia perfoliata; lower
leaves perfoliate, upper cordate-clasping, uppermost simply sessile.]
[Illustration: Fig. 163. Branch of a Honeysuckle, with
connate-perfoliate leaves.]
159. =Connate-perfoliate.= Such are the upper leaves of true
Honeysuckles. Here (Fig. 163) of the opposite and sessile leaves, some
pairs, especially the uppermost, in the course of their formation unite
around the stem, which thus seems to run through the disk formed by
their union.
[Illustration: Fig. 164. Rootstock and equitant leaves of Iris. 165. A
section across the cluster of leaves at the bottom, showing the
equitation.]
160. =Equitant Leaves.= While ordinary leaves spread horizontally, and
present one face to the sky and the other to the earth, there are some
that present their tip to the sky, and their faces right and left to the
horizon. Among these are the _equitant_ leaves of the Iris or
Flower-de-Luce. Inspection shows that each leaf was formed as if _folded
together lengthwise_, so that what would be the upper surface is
within, and all grown together, except next the bottom, where each leaf
covers the next younger one. It was from their straddling over each
other, like a man on horseback (as is seen in the cross-section, Fig.
165), that Linnaeus, with his lively fancy, called these _Equitant_
leaves.
161. =Leaves with no distinction of Petiole and Blade.= The leaves of
Iris just mentioned show one form of this. The flat but narrow leaves of
Jonquils, Daffodils, and the cylindrical leaf of Onions are other
instances. _Needle-shaped_ leaves, like those of the Pine, Larch, and
Spruce, and the _awl-shaped_ as well as the _scale-shaped_ leaves of
Junipers, Red Cedar, and Arbor-Vitae (Fig. 166), are examples.
[Illustration: Fig. 166. Branch of Arbor-Vitae, with awl-shaped and
scale-shaped leaves.]
162. =Phyllodia.= Sometimes an expanded _petiole_ takes the place of the
blade; as in numerous New Holland Acacias, some of which are now common
in greenhouses. Such counterfeit blades are called _phyllodia_,--meaning
leaf-like bodies. They may be known from true blades by their standing
edgewise, their margins being directed upwards and downwards; while in
true blades the faces look upwards and downwards; excepting in equitant
leaves, as already explained.
163. =Falsely Vertical Leaves.= These are apparent exceptions to the
rule, the blade standing edgewise instead of flatwise to the stem; but
this position comes by a twist of the stalk or the base of the blade.
Such leaves present the two faces about equally to the light. The
Compass-plant (Silphium laciniatum) is an example. So also the leaves of
Boltonia, of Wild Lettuce, and of a vast number of Australian Myrtaceous
shrubs and trees, which much resemble the phyllodia of the Acacias of
the same country. They are familiar in Callistemon, the Bottle-brush
Flower, and in Eucalyptus. But in the latter the leaves of the young
tree have the normal structure and position.
[Illustration: Fig. 167. The ambiguous leaf? (cladophyllum) of
Myrsiphyllum.]
[Illustration: Fig. 168. Same of Ruscus, or Butcher's Broom.]
164. =Cladophylla=, meaning _branch-leaves_. The foliage of Ruscus (the
Butcher's Broom of Europe) and of Myrsiphyllum of South Africa
(cultivated for decoration under the false name of Smilax) is peculiar
and puzzling. If these blades (Fig. 167, 168) are really leaves, they
are most anomalous in occupying the axil of another leaf, reduced to a
little scale. Yet they have an upper and lower face, as leaves should,
although they soon twist, so as to stand more or less edgewise. If they
are branches which have assumed exactly the form and office of leaves,
they are equally extraordinary in not making any further development.
But in Ruscus, flowers are borne on one face, in the axil of a little
scale: and this would seem to settle that they are branches. In
Asparagus just the same things as to position are thread-shaped and
branch-like.
Sec. 2. LEAVES OF SPECIAL CONFORMATION AND USE.
[Illustration: Fig. 169. A young Agave Americana, or Century-plant;
fleshy-leaved.]
165. =Leaves for Storage.= A leaf may at the same time serve both
ordinary and special uses. Thus in those leaves of Lilies, such as the
common White Lily, which spring from the bulb, the upper and green part
serves for foliage and elaborates nourishment, while the thickened
portion or bud-scale beneath serves for the storage of this nourishment.
The thread-shaped leaf of the Onion fulfils the same office, and the
nourishing matter it prepares is deposited in its sheathing base,
forming one of the concentric layers of the onion. When these layers, so
thick and succulent, have given up their store to the growing parts
within, they are left as thin and dry husks. In a Houseleek, an Aloe or
an Agave, the green color of the surface of the fleshy leaf indicates
that it is doing the work of foliage; the deeper-seated white portion
within is the storehouse of the nourishment which the green surface has
elaborated. So, also, the seed-leaves or cotyledons are commonly used
for storage. Some, as in one of the Maples, the Pea, Horse-chestnut,
Oak, etc., are for nothing else. Others, as in Beech and in our common
Beans, give faint indications of service as foliage also, chiefly in
vain. Still others, as in the Pumpkin and Flax, having served for
storage, develop into the first efficient foliage. Compare 11, 22-30,
and the accompanying figures.
[Illustration: Fig. 170. Series of bud-scales and foliage-leaves from a
developing bud of the Low Sweet Buckeye (AEsculus parviflora), showing
nearly complete gradation, from a scale to a compound leaf of five
leaflets; and that the scales answer to reduced petioles.]
166. =Leaves as Bud-Scales= serve to protect the forming parts within.
Having fulfilled this purpose they commonly fall off when the shoot
develops and foliage-leaves appear. Occasionally, as in Fig. 170, there
is a transition of bud-scales to leaves, which reveals the nature of the
former. The Lilac also shows a gradation from bud-scale to simple leaf.
In Cornus florida (the Flowering Dogwood), the four bud-scales which
through the winter protect the head of forming flowers remain until
blossoming, and then the base of each grows out into a large and very
showy petal-like leaf; the original dry scale is apparent in the notch
at the apex.
[Illustration: Fig. 171. Shoot of common Barberry, showing transition of
foliage-leaves to spines.]
167. =Leaves as Spines= occur in several plants. A familiar instance is
that of the common Barberry (Fig. 171). In almost any summer shoot, most
of the gradations may be seen between the ordinary leaves, with sharp
bristly teeth, and leaves which are reduced to a branching spine or
thorn. The fact that the spines of the Barberry produce a leaf-bud in
their axil also proves them to be leaves.
[Illustration: Fig. 172. Leaves of Solanum jasminoides, the petiole
adapted for climbing.]
[Illustration: Fig. 173. Leaf of Lathyrus Aphaca, consisting of a pair
of stipules and a tendril.]
168. =Leaves for Climbing= are various in adaptation. True
foliage-leaves serve this purpose; as in Gloriosa, where the attenuated
tip of a simple leaf (otherwise like that of a Lily) hooks around a
supporting object; or in Solanum jasminoides of the gardens (Fig. 172),
and in Maurandia, etc., where the leaf-stalk coils round and clings to a
support; or in the compound leaves of Clematis and of Adlumia, in which
both the leaflets and their stalks hook or coil around the support.
169. Or in a compound leaf, as in the Pea and most Vetches, and in
Cobaea, while the lower leaflets serve for foliage, some of the uppermost
are developed as tendrils for climbing (Fig. 167). In the common Pea
this is so with all but one or two pairs of leaflets.
170. In one European Vetch, the leaflets are wanting and the whole
petiole is a tendril, while the stipules become the only foliage (Fig.
173).
171. =Leaves as Pitchers=, or hollow tubes, are familiar in the common
Pitcher-plant or Side-saddle Flower (Sarracenia, Fig. 174) of our bogs.
These pitchers are generally half full of water, in which flies and
other insects are drowned, often in such numbers as to make a rich
manure for the plant. More curious are some of the southern species of
Sarracenia, which seem to be specially adapted to the capture and
destruction of flies and other insects.
[Illustration: Fig. 174. Leaf of Sarracenia purpurea, entire, and
another with the upper part cut off.]
172. The leaf of Nepenthes (Fig. 175) combines three structures and
uses. The expanded part below is foliage: this tapers into a tendril for
climbing; and this bears a pitcher with a lid. Insects are caught, and
perhaps digested, in the pitcher.
[Illustration: Fig. 175. Leaf of Nepenthes; foliage, tendril, and
pitcher combined.]
[Illustration: Fig. 176. Leaves of Dionaea; the trap in one of them open,
in the others closed.]
173. =Leaves as Fly-traps.= Insects are caught in another way, and more
expertly, by the most extraordinary of all the plants of this country,
the Dionaea or Venus's Fly-trap, which grows in the sandy bogs around
Wilmington, North Carolina. Here (Fig. 176) each leaf bears at its
summit an appendage which opens and shuts, in shape something like a
steel-trap, and operating much like one. For when open, no sooner does a
fly alight on its surface, and brush against any one of the two or three
bristles that grow there, than the trap suddenly closes, capturing the
intruder. If the fly escapes, the trap soon slowly opens, and is ready
for another capture. When retained, the insect is after a time moistened
by a secretion from minute glands of the inner surface, and is digested.
In the various species of Drosera or Sundew, insects are caught by
sticking fast to very viscid glands at the tip of strong bristles, aided
by adjacent gland-tipped bristles which bend slowly toward the captive.
The use of such adaptations and operations may be explained in another
place.
Sec. 3. STIPULES.
174. A leaf complete in its parts consists of blade, leaf-stalk or
petiole, and a pair of stipules. But most leaves have either fugacious
or minute stipules or none at all; many have no petiole (the blade being
_sessile_ or stalkless); some have no clear distinction of blade and
petiole; and many of these, such as those of the Onion and all phyllodia
(166), consist of petiole only.
175. The base of the petiole is apt to be broadened and flattened,
sometimes into thin margins, sometimes into a sheath which embraces the
stem at the point of attachment.
[Illustration: Fig. 177. Leaf of Red Clover: _st_, stipules, adhering to
the base of _p_, the petiole; _b_, blade of three leaflets.]
[Illustration: Fig. 178. Part of stem and leaf of Prince's-Feather
(Polygonum orientale) with the united sheathing stipules forming a
sheath or _ocrea_.]
[Illustration: Fig. 179. Terminal winter bud of Magnolia Umbrella,
natural size. 180. Outermost bud-scale (pair of stipules) detached.]
176. =Stipules= are such appendages, either wholly or partly separated
from the petiole. When quite separate they are said to be _free_, as in
Fig. 112. When attached to the base of the petiole, as in the Rose and
in Clover (Fig. 177), they are _adnate_. When the two stipules unite
and sheathe the stem above the insertion, as in Polygonum (Fig. 178),
this sheath is called an _Ocrea_ from its likeness to a greave or
leggin.
177. In Grasses, when the sheathing base of the leaf may answer to
petiole, the summit of the sheath commonly projects as a thin and short
membrane, like an ocrea: this is called a LIGULA or LIGULE.
178. When stipules are green and leaf-like they act as so much foliage.
In the Pea they make up no small part of the actual foliage. In a
related plant (Lathyrus Aphaca, Fig. 173), they make the whole of it,
the remainder of the leaf being tendril.
179. In many trees the stipules are the bud-scales, as in the Beech, and
very conspicuously in the Fig-tree, Tulip-tree, and Magnolia (Fig. 179).
These fall off as the leaves unfold.
180. The stipules are spines or prickles in Locust and several other
Leguminous trees and shrubs; they are tendrils in Smilax or Greenbrier.
Sec. 4. THE ARRANGEMENT OF LEAVES.
181. =Phyllotaxy=, meaning leaf-arrangement, is the study of the
position of leaves, or parts answering to leaves, upon the stem.
[Illustration: Fig. 181. Alternate leaves, in Linden, Lime-tree, or
Basswood.]
[Illustration: Fig. 182. Opposite leaves, in Red Maple.]
182. The technical name for the attachment of leaves to the stem is the
_insertion_. Leaves (as already noticed, 54) are _inserted_ in three
modes. They are
_Alternate_ (Fig. 181), that is, one after another, or in other words,
with only a single leaf to each node;
_Opposite_ (Fig. 182), when there is a pair to each node, the two
leaves in this case being always on opposite sides of the stem;
_Whorled_ or _Verticillate_ (Fig. 183) when there are more than two
leaves on a node, in which case they divide the circle equally between
them, forming a _Verticel_ or whorl. When there are three leaves in the
whorl, the leaves are one third of the circumference apart; when four,
one quarter, and so on. So the plan of opposite leaves, which is very
common, is merely that of whorled leaves, with the fewest leaves to the
whorl, namely, two.
[Illustration: Fig. 183. Whorled leaves of Galium.]
183. In both modes and in all their modifications, the arrangement is
such as to distribute the leaves systematically and in a way to give
them a good exposure to the light.
[Illustration: Fig. 184. A piece of stem of Larch with two clusters
(fascicles) of numerous leaves.]
[Illustration: Fig. 185. Piece of a branch of Pitch Pine, with three
leaves in a fascicle or bundle, in the axil of a thin scale which
answers to a primary leaf. The bundle is surrounded at the base by a
short sheath, formed of the delicate scales of the axillary bud.]
184. No two or more leaves ever grow from the same point. The so-called
_Fascicled_ or _Clustered_ leaves are the leaves of a branch the nodes
of which are very close, just as they are in the bud, so keeping the
leaves in a cluster. This is evident in the Larch (Fig. 184), in which
examination shows each cluster to be made up of numerous leaves crowded
on a spur or short axis. In spring there are only such clusters; but in
summer some of them lengthen into ordinary shoots with scattered
alternate leaves. So, likewise, each cluster of two or three
needle-shaped leaves in Pitch Pines (as in Fig. 185), or of five leaves
in White Pine, answers to a similar extremely short branch, springing
from the axil of a thin and slender scale, which represents a leaf of
the main shoot. For Pines produce two kinds of leaves,--1. primary, the
proper leaves of the shoots, not as foliage, but in the shape of
delicate scales in spring, which soon fall away; and 2. secondary, the
_fascicled_ leaves, from buds in the axils of the former, and these form
the actual foliage.
185. =Phyllotaxy of Alternate Leaves.= Alternate leaves are distributed
along the stem in an order which is uniform for each species. The
arrangement in all its modifications is said to be _spiral_, because, if
we draw a line from the _insertion_ (i. e. the point of attachment) of
one leaf to that of the next, and so on, this line will wind spirally
around the stem as it rises, and in the same species will always bear
the same number of leaves for each turn round the stem. That is, any two
successive leaves will always be separated from each other by an equal
portion of the circumference of the stem. The distance in _height_
between any two leaves may vary greatly, even on the same shoot, for
that depends upon the length of the _internodes_, or spaces between the
leaves; but the distance as measured around the circumference (in other
words, the _Angular Divergence_, or angle formed by any two successive
leaves) is uniformly the same.
186. =Two-ranked.= The greatest possible divergence is, of course, where
the second leaf stands on exactly the opposite side of the stem from the
first, the third on the side opposite the second, and therefore over the
first, and the fourth over the second. This brings all the leaves into
two ranks, one on one side of the stem and one on the other, and is
therefore called the _Two-ranked_ arrangement. It occurs in all
Grasses,--in Indian Corn, for instance; also, in the Basswood (Fig.
181). This is the simplest of all arrangements, and the one which most
widely distributes successive leaves, but which therefore gives the
fewest vertical ranks. Next is the
187. =Three-ranked= arrangement,--that of all Sedges, and of White
Hellebore. Here the second leaf is placed one third of the way round the
stem, the third leaf two thirds of the way round, the fourth leaf
accordingly directly over the first, the fifth over the second, and so
on. That is, three leaves occur in each turn round the stem, and they
are separated from each other by one third of the circumference. (Fig.
186, 187.)
[Illustration: Fig. 186. Two-ranked arrangement, shown in a piece of the
stalk of a Sedge, with the leaves cut off above their bases; the leaves
are numbered in order, from 1 to 6. 187. Diagram or cross-section of the
same, in one plane; the leaves similarly numbered; showing two cycles of
three.]
188. =Five-ranked= is the next in the series, and the most common. It is
seen in the Apple (Fig. 188), Cherry, Poplar, and the greater number of
trees and shrubs. In this case the line traced from leaf to leaf will
pass twice round the stem before it reaches a leaf situated directly
over any below (Fig. 189). Here the sixth leaf is over the first; the
leaves stand in five perpendicular ranks, with equal angular distance
from each other; and this distance between any two successive leaves is
just two fifths of the circumference of the stem.
[Illustration: Fig. 188. Shoot with its leaves 5-ranked, the sixth leaf
over the first; as in the Apple-tree.]
[Illustration: Fig. 189. Diagram of this arrangement, with a spiral line
drawn from the attachment of one leaf to the next, and so on; the parts
on the side turned from the eye are fainter.]
[Illustration: Fig. 190. A ground-plan of the same; the section of the
leaves similarly numbered; a dotted line drawn from the edge of one leaf
to that of the next marks out the spiral.]
189. The five-ranked arrangement is expressed by the fraction 2/5. This
fraction denotes the divergence of the successive leaves, i. e. the
angle they form with each other: the numerator also expresses the number
of turns made round the stem by the spiral line in completing one cycle
or set of leaves, namely, two; and the denominator gives the number of
leaves in each cycle, or the number of perpendicular ranks, namely,
five. In the same way the fraction 1/2 stands for the two-ranked mode,
and 1/3 for the three-ranked: and so these different sorts are expressed
by the series of fractions 1/2, 1/3, 2/5. Other cases follow in the same
numerical progression, the next being the
190. =Eight-ranked= arrangement. In this the ninth leaf stands over the
first, and three turns are made around the stem to reach it; so it is
expressed by the fraction 3/8. This is seen in the Holly, and in the
common Plantain. Then comes the
191. =Thirteen-ranked= arrangement, in which the fourteenth leaf is over
the first, after five turns around the stem. The common Houseleek (Fig.
191) is a good example.
192. The series so far, then, is 1/2, 1/3, 2/5, 3/8, 5/13; the numerator
and the denominator of each fraction being those of the two next
preceding ones added together. At this rate the next higher should be
8/21, then 13/34, and so on; and in fact just such cases are met with,
and (commonly) no others. These higher sorts are found in the Pine
Family, both in the leaves and the cones and in many other plants with
small and crowded leaves. But in those the number of the ranks, or of
leaves in each cycle, can only rarely be made out by direct inspection.
They may be indirectly ascertained, however, by studying the _secondary_
spirals, as they are called, which usually become conspicuous, at least
two series of them, one turning to the right and one to the left, as
shown in Fig. 191. For an account of the way in which the character of
the phyllotaxy may be deduced from the secondary spirals, see Structural
Botany, Chapter IV.
[Illustration: Fig. 191. A young plant of the Houseleek, with the leaves
(not yet expanded) numbered, and exhibiting the 13-ranked arrangement;
and showing secondary spirals.]
193. =Phyllotaxy of Opposite and whorled Leaves.= This is simple and
comparatively uniform. The leaves of each pair or whorl are placed over
the intervals between those of the preceding, and therefore under the
intervals of the pair or whorl next above. The whorls or pairs alternate
or cross each other, usually at right angles, that is, they _decussate_.
Opposite leaves, that is, whorls of two leaves only, are far commoner
than whorls of three or four or more members. This arrangement in
successive decussating pairs gives an advantageous distribution on the
stem in four vertical ranks. Whorls of three give six vertical ranks,
and so on. Note that in descriptive botany leaves in whorls of two are
simply called _opposite_ leaves; and that the term _verticillate_ or
_whorled_, is employed only for cases of more than two, unless the
latter number is specified.
[Illustration: Fig. 192. Opposite leaves of Euonymus, or Spindle-tree,
showing the successive pairs crossing each other at right angles.]
194. =Vernation or Praefoliation=, the disposition of the leaf-blades in
the bud, comprises two things; 1st, the way in which each separate leaf
is folded, coiled, or packed up in the bud; and 2d, the arrangement of
the leaves in the bud with respect to one another. The latter of course
depends very much upon the phyllotaxy, i. e. the position and order of
the leaves upon the stem. The same terms are used for it as for the
arrangement of the leaves of the flower in the flower-bud. See,
therefore, "AEstivation, or Praefloration."
195. As to each leaf separately, it is sometimes _straight_ and open in
vernation, but more commonly it is either _bent_, _folded_, or _rolled
up_. When the upper part is bent down upon the lower, as the young blade
in the Tulip-tree is bent upon the leaf-stalk, it is said to be
_Inflexed_ or _Reclined_ in vernation. When folded by the midrib so that
the two halves are placed face to face, it is _Conduplicate_ (Fig. 193),
as in the Magnolia, the Cherry, and the Oak. When folded back and forth
like the plaits of a fan, it is _Plicate_ or _Plaited_ (Fig. 194), as
in the Maple and Currant. If rolled, it may be so either from the tip
downwards, as in Ferns and the Sundew (Fig. 197), when in unrolling it
resembles the head of a crosier, and is said to be _Circinate_; or it
may be rolled up parallel with the axis, either from one edge into a
coil, when it is _Convolute_ (Fig. 195), as in the Apricot and Plum; or
rolled from both edges towards the midrib,--sometimes inwards, when it
is _Involute_ (Fig. 198), as in the Violet and Water-Lily; sometimes
outwards, when it is _Revolute_ (Fig. 196), in the Rosemary and Azalea.
The figures are diagrams, representing sections through the leaf, in the
way they were represented by Linnaeus.
[Illustration: Fig. 193. 194. 195. 196. 197. 198.]
Section VIII. FLOWERS.
196. Flowers are for the production of seed (16). Stems and branches,
which for a time put forth leaves for vegetation, may at length put
forth flowers for reproduction.
Sec. 1. POSITION AND ARRANGEMENT OF FLOWERS, OR INFLORESCENCE.
197. Flower-buds appear just where leaf-buds appear; that is, they are
either _terminal_ or _axillary_ (47-49). Morphologically, flowers answer
to shoots or branches, and their parts to leaves.
198. In the same species the flowers are usually from axillary buds
only, or from terminal buds only; but in some they are both axillary and
terminal.
199. =Inflorescence=, which is the name used by Linnaeus to signify mode
of flower-arrangement, is accordingly of three classes: namely,
_Indeterminate_, when the flowers are in the axils of leaves, that is,
are from axillary buds; _Determinate_, when they are from terminal buds,
and so _terminate_ a stem or branch; and _Mixed_, when these two are
combined.
200. =Indeterminate Inflorescence= (likewise, and for the same reason,
called _indefinite inflorescence_) is so named because, as the flowers
all come from axillary buds, the terminal bud may keep on growing and
prolong the stem indefinitely. This is so in Moneywort (Fig. 199).
[Illustration: Fig. 199. Piece of a flowering-stem of Moneywort
(Lysimachia nummularia,) with single flowers successively produced in
the axils of the leaves, from below upwards, as the stem grows on.]
201. When flowers thus arise singly from the axils of ordinary leaves,
they are _axillary_ and _solitary_, not collected into flower-clusters.
202. But when several or many flowers are produced near each other, the
accompanying leaves are apt to be of smaller size, or of different shape
or character: then they are called BRACTS, and the flowers thus brought
together form a cluster. The kinds of flower-clusters of the
indeterminate class have received distinct names, according to their
form and disposition. They are principally _Raceme_, _Corymb_, _Umbel_,
_Spike_, _Head_, _Spadix_, _Catkin_, and _Panicle_.
203. In defining these it will be necessary to use some of the following
terms of descriptive botany which relate to inflorescence. If a flower
is stalkless, i. e. sits directly in the axil or other support, it is
said to be _sessile_. If raised on a naked stalk of its own (as in Fig.
199) it is _pedunculate_, and the stalk is a PEDUNCLE.
204. A peduncle on which a flower-cluster is raised is a _Common
peduncle_. That which supports each separate flower of the cluster is a
_Partial peduncle_, and is generally called a PEDICEL. The portion of
the general stalk along which flowers are disposed is called the _Axis
of inflorescence_, or, when covered with sessile flowers, the _Rhachis_
(back-bone), and sometimes the _Receptacle_. The leaves of a
flower-cluster generally are termed BRACTS. But when bracts of different
orders are to be distinguished, those on the common peduncle or axis,
and which have a flower in their axil, keep the name of _bracts_; and
those on the pedicels or partial flower-stalks, if any, that of
BRACTLETS or _Bracteoles_. The former is the preferable English name.
[Illustration: Fig. 200. A raceme, with a general peduncle (_p_),
pedicels (_p'_), bracts (_b_), and bractlets (_b'_). Plainly the bracts
here answer to the leaves in Fig. 199.]
205. =A Raceme= (Fig. 200) is that form of flower-cluster in which the
flowers, each on their own foot-stalk or pedicel, are arranged along the
sides of a common stalk or axis of inflorescence; as in the Lily of the
Valley, Currant, Barberry, one section of Cherry, etc. Each flower comes
from the axil of a small leaf, or bract, which, however, is often so
small that it might escape notice, and even sometimes (as in the Mustard
Family) disappears altogether. The lowest blossoms of a raceme are of
course the oldest, and therefore open first, and the order of blossoming
is _ascending_ from the bottom to the top. The summit, never being
stopped by a terminal flower, may go on to grow, and often does so (as
in the common Shepherd's Purse), producing lateral flowers one after
another for many weeks.
[Illustration: Fig. 201. A raceme. 202. A corymb. 203. An umbel.]
206. =A Corymb= (Fig. 202) is the same as a raceme, except that it is
flat and broad, either convex, or level-topped. That is, a raceme
becomes a corymb by lengthening the lower pedicels while the uppermost
remain shorter. The axis of a corymb is short in proportion to the lower
pedicels. By extreme shortening of the axis the corymb may be converted
into
207. =An Umbel= (Fig. 203) as in the Milkweed, a sort of flower-cluster
where the pedicels all spring apparently from the same point, from the
top of the peduncle, so as to resemble, when spreading, the rays of an
umbrella; whence the name. Here the pedicels are sometimes called the
_Rays_ of the umbel. And the bracts, when brought in this way into a
cluster or circle, form what is called an INVOLUCRE.
208. The corymb and the umbel being more or less level-topped, bringing
the flowers into a horizontal plane or a convex form, the ascending
order of development appears as _Centripetal_. That is, the flowering
proceeds from the margin or circumference regularly towards the centre;
the lower flowers of the former answering to the outer ones of the
latter.
209. In these three kinds of flower-clusters, the flowers are raised on
conspicuous _pedicels_ (204) or stalks of their own. The shortening of
these pedicels, so as to render the flowers _sessile_ or nearly so,
converts a raceme into a _Spike_, and a corymb or an umbel into a
_Head_.
210. =A Spike= is a flower cluster with a more or less lengthened axis,
along which the flowers are sessile or nearly so; as in the Plantain
(Fig. 204).
[Illustration: Fig. 204. Spike of the common Plantain or Ribwort.]
211. =A Head= (_Capitulum_) is a round or roundish cluster of flowers,
which are sessile on a very short axis or receptacle, as in the
Button-ball, Button-bush (Fig. 205), and Red Clover. It is just what a
spike would become if its axis were shortened; or an umbel, if its
pedicels were all shortened until the flowers became sessile. The head
of the Button-bush is naked; but that of the Thistle, of the Dandelion,
and the like, is surrounded by empty bracts, which form an _Involucre_.
Two particular forms of the spike and the head have received particular
names, namely, the _Spadix_ and the _Catkin_.
[Illustration: Fig. 205. Head of the Button-bush (Cephalanthus).]
212. =A Spadix= is a fleshy spike or head, with small and often
imperfect flowers, as in the Calla, Indian Turnip, (Fig. 206), Sweet
Flag, etc. It is commonly surrounded or embraced by a peculiar
enveloping leaf, called a SPATHE.
[Illustration: Fig. 206. Spadix and spathe of the Indian Turnip; the
latter cut through below.]
213. =A Catkin, or Ament=, is the name given to the scaly sort of spike
of the Birch (Fig. 207) and Alder, the Willow and Poplar, and one sort
of flower-clusters of the Oak, Hickory, and the like,--the so-called
_Amentaceous_ trees.
[Illustration: Fig. 207. Catkin, or Ament, of Birch.]
214. _Compound_ flower-clusters of these kinds are not uncommon. When
the stalks which in the simple umbel are the pedicels of single flowers
themselves branch into an umbel, a _Compound Umbel_ is formed. This is
the inflorescence of Caraway (Fig. 208), Parsnip, and almost all of the
great family of Umbelliferous (umbel-bearing) plants.
[Illustration: Fig. 208. Compound Umbel of Caraway.]
215. The secondary or partial umbels of a compound umbel are UMBELLETS.
When the umbellets are subtended by an involucre, this secondary
involucre is called an INVOLUCEL.
216. A _Compound raceme_ is a cluster of racemes racemosely arranged, as
in Smilacina racemosa. A _compound corymb_ is a corymb some branches of
which branch again in the same way, as in Mountain Ash. A _compound
spike_ is a spicately disposed cluster of spikes.
[Illustration: Fig. 209. Diagram of a simple panicle.]
217. =A Panicle=, such as that of Oats and many Grasses, is a compound
flower-cluster of a more or less open sort which branches with apparent
irregularity, neither into corymbs nor racemes. Fig. 209 represents the
simplest panicle. It is, as it were, a raceme of which some of the
pedicels have branched so as to bear a few flowers on pedicels of their
own, while others remain simple. A _compound panicle_ is one that
branches in this way again and again.
[Illustration: Fig. 210. Diagram of an opposite-leaved plant, with a
single terminal flower. 211. Same, with a cyme of three flowers; _a_,
the first flower, of the main axis; _b b_, those of branches. 212. Same,
with flowers also of the third order, _c c_.]
218. =Determinate Inflorescence= is that in which the flowers are from
terminal buds. The simplest case is that of a solitary terminal flower,
as in Fig. 210. This stops the growth of the stem; for its terminal bud,
becoming a blossom, can no more lengthen in the manner of a leaf-bud.
Any further growth must be from axillary buds developing into branches.
If such branches are leafy shoots, at length terminated by single
blossoms, the inflorescence still consists of solitary flowers at the
summit of stem and branches. But if the flowering branches bear only
bracts in place of ordinary leaves, the result is the kind of
flower-cluster called
219. =A Cyme.= This is commonly a flat-topped or convex flower-cluster,
like a corymb, only the blossoms are from terminal buds. Fig. 211
illustrates the simplest cyme in a plant with opposite leaves, namely,
with three flowers. The middle flower, _a_, terminates the stem; the two
others, _b b_, terminate branches, one from the axil of each of the
uppermost leaves; and being later than the middle one, the flowering
proceeds from the centre outwards, or is _Centrifugal_. This is the
opposite of the indeterminate mode, or that where all the flower-buds
are axillary. If flowering branches appear from the axils below, the
lower ones are the later, so that the order of blossoming continues
_centrifugal_ or, which is the same thing, _descending_, as in Fig. 213,
making a sort of reversed raceme or _false raceme_,--a kind of cluster
which is to the true raceme just what the flat cyme is to the corymb.
[Illustration: Fig. 213. Diagram of a simple cyme in which the axis
lengthens, so as to take the form of a raceme.]
220. Wherever there are bracts or leaves, buds may be produced from
their axils and appear as flowers. Fig. 212 represents the case where
the branches, _b b_, of Fig. 211, each with a pair of small leaves or
bracts about their middle, have branched again, and produced the
branchlets and flowers _c c_, on each side. It is the continued
repetition of this which forms the full or compound cyme, such as that
of the Laurestinus, Hobble-bush, Dogwood, and Hydrangea (Fig. 214).
[Illustration: Fig. 214. Compound cyme of Hydrangea arborescens, with
neutral enlarged flowers round the circumference.]
221. =A Fascicle= (meaning a bundle), like that of the Sweet William and
Lychnis of the gardens, is only a cyme with the flowers much crowded.
222. =A Glomerule= is a cyme still more compacted, so as to imitate a
head. It may be known from a true head by the flowers not expanding
centripetally, that is, not from the circumference towards the centre.
223. The illustrations of determinate or _cymose_ inflorescence have
been taken from plants with opposite leaves, which give rise to the most
regular cymes. But the Rose, Cinquefoil, Buttercup, etc., with alternate
leaves, furnish also good examples of cymose inflorescence.
224. =A Cymule= (or diminutive cyme) is either a reduced small cyme of
few flowers, or a branch of a compound cyme, i. e. a partial cyme.
225. =Scorpioid= or =Helicoid Cymes=, of various sorts, are forms of
determinate inflorescence (often puzzling to the student) in which one
half of the ramification fails to appear. So that they may be called
_incomplete cymes_. The commoner forms may be understood by comparing a
complete cyme, like that of Fig. 215 with Fig. 216, the diagram of a
cyme of an opposite-leaved plant, having a series of terminal flowers
and the axis continued by the development of a branch in the axil of
only one of the leaves at each node. The dotted lines on the left
indicate the place of the wanting branches, which if present would
convert this _scorpioid cyme_ into the complete one of Fig. 215. Fig.
217 is a diagram of similar inflorescence with alternate leaves. Both
are kinds of _false racemes_ (219). When the bracts are also wanting in
such cases, as in many Borragineous plants, the true nature of the
inflorescence is very much disguised.
[Illustration: Fig. 215. A complete forking cyme of an Arenaria, or
Chickweed.]
[Illustration: Fig. 216. Diagram of a scorpioid cyme, with opposite
leaves or bracts.]
[Illustration: Fig. 217. Diagram of analogous scorpioid cyme, with
alternate leaves or bracts.]
226. These distinctions between determinate and indeterminate
inflorescence, between corymbs and cymes, and between the true and the
false raceme and spike, were not recognized by botanists much more than
half a century ago, and even now are not always attended to in
descriptions. It is still usual and convenient to describe rounded or
flat-topped and open ramification as _corymbose_, even when essentially
cymose; also to call the reversed or false racemes or spikes by these
(strictly incorrect) names.
227. =Mixed Inflorescence= is that in which the two plans are mixed or
combined in compound clusters. A _mixed panicle_ is one in which, while
the primary ramification is of the indeterminate order, the secondary or
ultimate is wholly or partly of the determinate order. A contracted or
elongated inflorescence of this sort is called a THYRSUS. Lilac and
Horse-chestnut afford common examples of mixed inflorescence of this
sort. When loose and open such flower-clusters are called by the general
name of _Panicles_. The heads of Compositae are centripetal; but the
branches or peduncles which bear the heads are usually of centrifugal
order.
Sec. 2. PARTS OR ORGANS OF THE FLOWER.
228. These were simply indicated in Section II. 16. Some parts are
necessary to seed-bearing; these are _Essential Organs_, namely, the
_Stamens_ and _Pistils_. Others serve for protection or for attraction,
often for both. Such are the leaves of the Flower, or the _Floral
Envelopes_.
229. =The Floral Envelopes=, taken together, are sometimes called the
PERIANTH, also _Perigone_, in Latin form _Perigonium_. In a flower which
possesses its full number of organs, the floral envelopes are of two
kinds, namely, an outer circle, the CALYX, and an inner, the COROLLA.
230. =The Calyx= is commonly a circle of green or greenish leaves, but
not always. It may be the most brightly colored part of the blossom.
Each calyx-leaf or piece is called a SEPAL.
231. =The Corolla= is the inner circle of floral envelopes or
flower-leaves, usually of delicate texture and _colored_, that is, of
some other color than green. Each corolla-leaf is called a PETAL.
232. There are flowers in abundance which consist wholly of floral
envelopes. Such are the so-called full _double flowers_, of which the
choicer roses and camellias of the cultivator are familiar examples. In
them, under the gardener's care and selection, petals have taken the
place of both stamens and pistils. These are monstrous or unnatural
flowers, incapable of producing seed, and subservient only to human
gratification. Their common name of _double_ flowers is not a sensible
one: except that it is fixed by custom, it were better to translate
their Latin name, _flores pleni_, and call them _full flowers_, meaning
full of leaves.
233. Moreover, certain plants regularly produce _neutral flowers_,
consisting of floral envelopes only. In Fig. 214, some are seen around
the margin of the cyme in Hydrangea. They are likewise familiar in the
Hobble-bush and in Wild-Cranberry tree, Viburnum Oxycoccus; where they
form an attractive setting to the cluster of small and comparatively
inconspicuous perfect flowers which they adorn. In the Guelder Rose, or
Snow-ball of ornamental cultivation, all or most of the blossoms of this
same shrub are transformed into neutral flowers.
[Illustration: Fig. 218. A _flos plenus_, namely, a full double flower
of Rose.]
234. =The Essential Organs= are likewise of two kinds, placed one above
or within the other; namely, first, the STAMENS or fertilizing organs,
and second, the PISTILS, which are to be fertilized and bear the seeds.
[Illustration: Fig. 219. A stamen: _a_, filament; _b_, anther,
discharging pollen.]
[Illustration: Fig. 220. A pistil; with ovary, _a_, half cut away, to
show the contained ovules; _b_, style; _c_, stigma.]
235. =A Stamen= consists of two parts, namely, the FILAMENT or stalk
(Fig. 219 _a_), and the ANTHER (_b_). The latter is the only essential
part. It is a case, commonly with two lobes or cells, each opening
lengthwise by a slit, at the proper time, and discharging a powder or
dust-like substance, usually of a yellow color. This powder is the
POLLEN, or fertilizing matter, to produce which is the office of the
stamen.
236. =A Pistil= (Fig. 220, 221) when complete, has three parts; OVARY,
STYLE, and STIGMA. The _Ovary_, at base, is the hollow portion, which
contains one or more OVULES or rudimentary seeds. The _Style_ is the
tapering portion above: the _Stigma_ is a portion of the style, usually
its tip, with moist naked surface, upon which grains of pollen may lodge
and adhere, and thence make a growth which extends down to the ovules.
When there is no style then the stigma occupies the tip of the ovary.
[Illustration: Fig. 221. Model of a simple pistil, with ovary cut across
and slightly opened ventrally, to show the ovules and their attachment.]
237. =The Torus= or =Receptacle= is the end of the flower-stalk, or the
portion of axis or stem out of which the several organs of the flower
grow, upon which they are borne (Fig. 223).
[Illustration: Fig. 222. Flower of Sedum ternatum, a Stonecrop.]
[Illustration: Fig. 223. Parts of same, two of each kind, separated and
displayed; the torus or receptacle in the centre; _a_, a sepal; _b_, a
petal; _c_, a stamen; _d_, a pistil.]
238. The parts of the flower are thus disposed on the receptacle or axis
essentially as are leaves upon a very short stem; first the sepals, or
outer floral leaves; then the petals or inner floral leaves; then the
stamens; lastly, at summit or centre, the pistils, when there are two or
more of them, or the single pistil, when only one. Fig. 223 shows the
organs displayed, two of each kind, of such a simple and symmetrical
flower as that of a Sedum or Stonecrop, Fig. 222.
Sec. 3. PLAN OF FLOWER.
239. All flowers are formed upon one general plan, but with almost
infinite variations, and many disguises. This common plan is best
understood by taking for a type, or standard for comparison, some
_perfect_, _complete_, _regular_, and _symmetrical_ blossom, and one as
simple as such a blossom could well be. Flowers are said to be
_Perfect_ (_hermaphrodite_), when provided with both kinds of essential
organs, i. e. with both stamens and pistils.
_Complete_, when, besides, they have the two sets of floral envelopes,
namely, calyx and corolla. Such are completely furnished with all that
belongs to a flower.
_Regular_, when all the parts of each set are alike in shape and size.
_Symmetrical_, when there is an equal number of parts in each set or
circle of organs.
240. Flax-flowers were taken for a pattern in Section II. 16. But in
them the five pistils have their ovaries as it were consolidated into
one body. Sedum, Fig. 222, has the pistils and all the other parts free
from such combination. The flower is perfect, complete, regular, and
symmetrical, but is not quite as simple as it might be; for there are
twice as many stamens as there are of the other organs. Crassula, a
relative of Sedum, cultivated in the conservatories for winter
blossoming (Fig. 224) is simpler, being _isostemonous_, or with just as
many stamens as petals or sepals, while Sedum is _diplostemonous_,
having double that number: it has, indeed, two sets of stamens.
[Illustration: Fig. 224. Flower of a Crassula. 225. Diagram or
ground-plan of same.]
241. =Numerical Plan.= A certain number either runs through the flower
or is discernible in some of its parts. This number is most commonly
either five or three, not very rarely four, occasionally two. Thus the
_ground-plan_ of the flowers thus far used for illustration is five.
That of Trillium (Fig. 226, 227) is three, as it likewise is as really,
if not as plainly, in Tulips and Lilies, Crocus, Iris, and all that
class of blossoms. In some Sedums all the flowers are in fours. In
others the first flowers are on the plan of five, the rest mostly on the
plan of four, that is, with four sepals, four petals, eight stamens (i.
e. twice four), and four pistils. Whatever the ground number may be, it
runs through the whole in symmetrical blossoms.
[Illustration: Fig. 226. Flower of a Trillium; its parts in threes.]
[Illustration: Fig. 227. Diagram of flower of Trillium. In this, as in
all such diagrams of cross-section of blossoms, the parts of the outer
circle represent the calyx; the next, corolla; within, stamens (here in
two circles of three each, and the cross-section is through the
anthers); in the centre, section of three ovaries joined into a compound
one of three cells.]
242. =Alternation of the successive Circles.= In these flowers the parts
of the successive circles _alternate_; and such is the rule. That is,
the petals stand over the intervals between the sepals; the stamens,
when of the same number, stand over the intervals between the petals; or
when twice as many, as in the Trillium, the outer set alternates with
the petals, and the inner set, alternating with the other, of course
stands before the petals; and the pistils alternate with these. This is
just as it should be on the theory that the circles of the blossom
answer to whorls of leaves, which alternate in this way. While in such
flowers the circles are to be regarded as whorls, in others they are
rather to be regarded as condensed spirals of alternate leaves. But,
however this may be, in the mind of a morphological botanist,
243. =Flowers are altered Branches=, and their parts, therefore, altered
leaves. That is, certain buds, which might have grown and lengthened
into a leafy branch, do, under other circumstances and to accomplish
other purposes, develop into blossoms. In these the axis remains short,
nearly as it is in the bud; the leaves therefore remain close together
in sets or circles; the outer ones, those of the calyx, generally
partake more or less of the character of foliage; the next set are more
delicate, and form the corolla, while the rest, the stamens and pistils,
appear under forms very different from those of ordinary leaves, and are
concerned in the production of seed. This view gives to Botany an
interest which one who merely notices the shape and counts the parts of
blossoms, without understanding their plan, has no conception of.
244. That flowers answer to branches may be shown, first, from their
position. As explained in the section on Inflorescence, flowers arise
from the same places as branches, and from no other; flower-buds, like
leaf-buds, appear either on the summit of a stem, that is, as a terminal
bud, or in the axil of a leaf, as an axillary bud. And, as the plan of a
symmetrical flower shows, the arrangement of the parts on their axis or
receptacle is that of leaves upon the stem.
245. That the sepals and petals are of the nature of leaves is evident
from their appearance; they are commonly called the leaves of the
flower. The calyx is most generally green in color, and foliaceous
(leaf-like) in texture. And though the corolla is rarely green, yet
neither are proper leaves always green. In our wild Painted-cup, and in
some scarlet Sages, common in gardens, the leaves just under the flowers
are of the brightest red or scarlet, often much brighter-colored than
the corolla itself. And sometimes (as in many Cactuses, and in Carolina
Allspice) there is such a regular gradation from the last leaves of the
plant (bracts or bractlets) into the leaves of the calyx, that it is
impossible to say where the one ends and the other begins. If sepals are
leaves, so also are petals; for there is no clearly fixed limit between
them. Not only in the Carolina Allspice and Cactus (Fig. 229), but in
the Water-Lily (Fig. 228) and in a variety of flowers with more than one
row of petals, there is such a complete transition between calyx and
corolla that no one can surely tell how many of the leaves belong to the
one and how many to the other.
[Illustration: Fig. 228. Series of sepals, petals, and stamens of White
Water-Lily, showing the transitions.]
[Illustration: Fig. 229. A Cactus blossom.]
246. That stamens are of the same general nature as petals, and
therefore a modification of leaves, is shown by the gradual transitions
that occur between the one and the other in many blossoms; especially in
cultivated flowers, such as Roses and Camellias, when they begin to
_double_, that is, to change their stamens into petals. Some wild and
natural flowers show the same interesting transitions. The Carolina
Allspice and the White Water-Lily exhibit complete gradations not only
between sepals and petals, but between petals and stamens. The sepals of
our Water-Lily are green outside, but white and petal-like on the
inside; the petals, in many rows, gradually grow narrower towards the
centre of the flower; some of these are tipped with a trace of a yellow
anther, but still are petals; the next are more contracted and
stamen-like, but with a flat petal-like filament; and a further
narrowing of this completes the genuine stamen.
247. Pistils and stamens now and then change into each other in some
Willows; pistils often turn into petals in cultivated flowers; and in
the Double Cherry they are occasionally replaced by small green leaves.
Sometimes a whole blossom changes into a cluster of green leaves, as in
the "green roses" occasionally noticed in gardens, and sometimes it
degenerates into a leafy branch. So the botanist regards pistils also as
answering to leaves; that is, to single leaves when simple and separate,
to a whorl of leaves when conjoined.
Sec. 4. MODIFICATIONS OF THE TYPE.
248. =The Deviations=, as they may be called, from the assumed type or
pattern of flower are most various and extensive. The differences
between one species and another of the same genus are comparatively
insignificant; those between different genera are more striking; those
between different families and classes of plants more and more profound.
They represent different adaptations to conditions or modes of life,
some of which have obvious or probable utilities, although others are
beyond particular explanation. The principal modifications may be
conveniently classified. First those which in place of perfect
(otherwise called _hermaphrodite_ or bisexual) flowers, give origin to
249. =Unisexual, or Separated, or Diclinous Flowers=, _imperfect_
flowers, as they have been called in contradistinction to perfect
flowers; but that term is too ambiguous. In these some flowers want the
stamens, while others want the pistils. Taking hermaphrodite flowers as
the pattern, it is natural to say that the missing organs are
_suppressed_. This expression is justified by the very numerous cases in
which the missing parts are _abortive_, that is, are represented by
rudiments or vestiges, which serve to exemplify the plan, although
useless as to office. Unisexual flowers are
_Monoecious_ (or _Monoicous_, i. e. of one household), when flowers of
both sorts or sexes are produced by the same individual plant, as in the
Ricinus or Castor-oil Plant, Fig. 230.
_Dioecious_ (or _Dioicous_, i. e. of separate households), when the
two kinds are borne on different plants; as in Willows, Poplars, Hemp,
and Moonseed, Fig. 231, 232.
_Polygamous_, when the flowers are some of them perfect, and some
staminate or pistillate only.
[Illustration: Fig. 230. Unisexual flowers of Castor-oil plant: _s_,
staminate flower; _p_, pistillate flower.]
[Illustration: Fig. 231, staminate, and 232, pistillate flower of
Moonseed.]
250. A blossom having stamens and no pistil is a _Staminate_ or _Male_
flower. Sometimes it is called a _Sterile_ flower, not appropriately,
for other flowers may equally be sterile. One having pistil but no
stamens is a _Pistillate_ or _Female_ flower.
[Illustration: Fig. 233. Flower of Anemone Pennsylvanica; apetalous,
hermaphrodite.]
[Illustration: Fig. 234. Flower of Saururus or Lizard's-tail; naked, but
hermaphrodite.]
251. =Incomplete Flowers= are so named in contradistinction to complete:
they want either one or both of the floral envelopes. Those of Fig. 230
are incomplete, having calyx but no corolla. So is the flower of Anemone
(Fig. 233), although its calyx is colored like a corolla. The flowers of
Saururus or Lizard's-tail, although perfect, have neither calyx nor
corolla (Fig. 234). Incomplete flowers, accordingly, are
_Naked_ or _Achlamydeous_, destitute of both floral envelopes, as in
Fig. 234, or
_Apetalous_, when wanting only the corolla. The case of corolla present
and calyx wholly wanting is extremely rare, although there are seeming
instances. In fact, a single or simple perianth is taken to be a calyx,
unless the absence or abortion of a calyx can be made evident.
[Illustration: Fig. 235. Flower of Mustard. 236. Its stamens and pistil
separate and enlarged.]
[Illustration: Fig. 237. Flower of a Violet. 238. Its calyx and corolla
displayed: the five smaller parts are the sepals; the five intervening
larger ones are the petals.]
252. In contradistinction to regular and symmetrical, very many flowers
are
_Irregular_, that is, with the members of some or all of the floral
circles unequal or dissimilar, and
_Unsymmetrical_, that is, when the circles of the flower or some of them
differ in the number of their members. (Symmetrical and unsymmetrical
are used in a different sense in some recent books, but the older use
should be adhered to). Want of numerical symmetry and irregularity
commonly go together; and both are common. Indeed, few flowers are
entirely symmetrical beyond calyx, corolla, and perhaps stamens; and
probably no irregular blossoms are quite symmetrical.
253. =Irregular and Unsymmetrical Flowers= may therefore be illustrated
together, beginning with cases which are comparatively free from other
complications. The blossom of Mustard, and of all the very natural
family which it represents (Fig. 235, 236), is regular but unsymmetrical
in the stamens. There are four equal sepals, four equal petals; but six
stamens, and only two members in the pistil, which for the present may
be left out of view. The want of symmetry is in the stamens. These are
in two circles, an outer and an inner. The outer circle consists of two
stamens only; the inner has its proper number of four. The flower of
Violet, which is on the plan of five, is symmetrical in calyx, corolla,
and stamens, inasmuch as each of these circles consists of five members;
but it is conspicuously irregular in the corolla, one of the petals
being very different from the rest.
[Illustration: Fig. 239. Flower of a Larkspur. 240. Its calyx and
corolla displayed; the five larger parts are the sepals; the four
smaller, of two shapes, are the petals; the place of the fifth petal is
vacant. 241. Diagram of the same; the place for the missing petal marked
by a dotted line.]
[Illustration: Fig. 242. Flower of a Monkshood. 243. Its parts
displayed; five sepals, the upper forming the hood; the two lateral
alike, broad and flat; the two lower small. The two pieces under the
hood represent the corolla, reduced to two odd-shaped petals; in centre
the numerous stamens and three pistils. 244. Diagram of the calyx and
corolla; the three dotted lines in the place of missing petals.]
254. The flowers of Larkspur, and of Monkshood or Aconite, which are
nearly related, are both strikingly irregular in calyx and corolla, and
considerably unsymmetrical. In Larkspur (Fig. 239-241) the irregular
calyx consists of five sepals, one of which, larger than the rest, is
prolonged behind into a large sac or spur; but the corolla is of only
four petals (of two shapes),--the fifth, needed to complete the
symmetry, being left out. And the Monkshood (Fig. 242-244) has five very
dissimilar sepals, and a corolla of only two very small and
curiously-shaped petals,--the three needed to make up the symmetry being
left out. The stamens in both are out of symmetry with the ground-plan,
being numerous. So are the pistils, which are usually diminished to
three, sometimes to two or to one.
255. =Flowers with Multiplication of Parts= are very common. The stamens
are indefinitely numerous in Larkspur and in Monkshood (Fig. 242, 243),
while the pistils are fewer than the ground-plan suggests. Most
Cactus-flowers have all the organs much increased in number (Fig. 229),
and so of the Water-Lily. In Anemone (Fig. 233) the stamens and pistils
are multiplied while the petals are left out. In Buttercups or Crowfoot,
while the sepals and petals conform to the ground-plan of five, both
stamens and pistils are indefinitely multiplied (Fig. 245).
[Illustration: Fig. 245. Flower of Ranunculus bulbosus, or Buttercup, in
section.]
256. =Flowers modified by Union of Parts=, so that these parts more or
less lose the appearance of separate leaves or other organs growing out
of the end of the stem or receptacle, are extremely common. There are
two kinds of such union, namely:--
_Coalescence_ of parts of the same circle by their contiguous margins;
and
_Adnation_, or the union of adjacent circles or unlike parts.
257. =Coalescence= is not rare in leaves, as in the upper pairs of
Honeysuckles, Fig. 163. It may all the more be expected in the crowded
circles or whorls of flower-leaves. Datura or Stramonium (Fig. 246)
shows this coalescence both in calyx and corolla, the five sepals and
the five petals being thus united to near their tips, each into a tube
or long and narrow cup. These unions make needful the following terms:--
_Gamopetalous_, said of a corolla the petals of which are thus
coalescent into one body, whether only at base or higher. The union may
extend to the very summit, as in Morning Glory and the like (Fig. 247),
so that the number of petals in it may not be apparent. The old name for
this was _Monopetalous_, but that means "one-petalled;" while
gamopetalous means "petals united," and therefore is the proper term.
[Illustration: Fig. 246. Flower of Datura Stramonium; gamosepalous and
gamopetalous.]
[Illustration: Fig. 247. Funnelform corolla of a common Morning Glory,
detached from its polysepalous calyx.]
_Polypetalous_ is the counterpart term, to denote a corolla of
_distinct_, that is, separate petals. As it means "many petalled," it is
not the best possible name, but it is the old one and in almost
universal use.
_Gamosepalous_ applies to the calyx when the sepals are in this way
united.
_Polysepalous_, to the calyx when of separate sepals or calyx-leaves.
258. Degree of union or of separation in descriptive botany is expressed
in the same way as is the lobing of leaves (139). See Fig. 249-253, and
the explanations.
259. A corolla when gamopetalous commonly shows a distinction (well
marked in Fig. 249-251) between a contracted tubular portion below, the
TUBE, and the spreading part above, the BORDER or LIMB. The junction
between tube and limb, or a more or less enlarged upper portion of the
tube between the two, is the THROAT. The same is true of the calyx.
260. Some names are given to particular forms of the gamopetalous
corolla, applicable also to a gamosepalous calyx, such as
_Wheel-shaped_, or _Rotate_; when spreading out at once, without a tube
or with a very short one, something in the shape of a wheel or of its
diverging spokes, Fig. 252, 253.
_Salver-shaped_, or _Salver-form_; when a flat-spreading border is
raised on a narrow tube, from which it diverges at right angles, like
the salver represented in old pictures, with a slender handle beneath,
Fig. 249-251, 255.
[Illustration: Fig. 248. Polypetalous corolla of Soapwort, of five
petals with long claws or stalk-like bases.]
[Illustration: Fig. 249. Flower of Standing Cypress (Gilia
coronopifolia); gamopetalous: the tube answering to the long claws in
248, except that they are coalescent: the limb or border (the spreading
part above) is _five-parted_, that is, the petals not there united
except at very base.]
[Illustration: Fig. 250. Flower of Cypress-vine (Ipomoea Quamoclit);
like preceding, but limb _five-lobed_.]
[Illustration: Fig. 251. Flower of Ipomoea coccinea; limb almost
_entire_.]
[Illustration: Fig. 252. Wheel-shaped or rotate and five-parted corolla
of Bittersweet, Solanum Dulcamara. 253. Wheel-shaped and five-lobed
corolla of Potato.]
_Bell-shaped_, or _Campanulate_; where a short and broad tube widens
upward, in the shape of a bell, as in Fig. 254.
[Illustration: Fig. 254. Flower of a Campanula or Harebell, with a
campanulate or bell-shaped corolla; 255, of a Phlox, with salver-shaped
corolla; 256, of Dead Nettle (Lamium), with labiate _ringent_ (or
gaping) corolla; 257, of Snapdragon, with labiate _personate_ corolla;
258, of Toad-Flax, with a similar corolla spurred at the base.]
_Funnel-shaped_, or _Funnelform_; gradually spreading at the summit of a
tube which is narrow below, in the shape of a funnel or tunnel, as in
the corolla of the common Morning Glory (Fig. 247) and of the Stramonium
(Fig. 246).
_Tubular_; when prolonged into a tube, with little or no spreading at
the border, as in the corolla of the Trumpet Honeysuckle, the calyx of
Stramonium (Fig. 246), etc.
261. Although sepals and petals are usually all blade or lamina (123),
like a sessile leaf, yet they may have a contracted and stalk-like base,
answering to petiole. This is called its CLAW, in Latin _Unguis_.
_Unguiculate_ petals are universal and strongly marked in the Pink
tribe, as in Soapwort (Fig. 248).
[Illustration: Fig. 259. Unguiculate (clawed) petal of a Silene; with a
two-parted crown.]
[Illustration: Fig. 260. A small Passion-flower, with crown of slender
threads.]
262. Such petals, and various others, may have an outgrowth of the inner
face into an appendage or fringe, as in Soapwort, and in Silene (Fig.
259), where it is at the junction of claw and blade. This is called a
CROWN, or _Corona_. In Passion-flowers (Fig. 260) the crown consists of
numerous threads on the base of each petal.
[Illustration: Fig. 261. Front view of a papilionaceous corolla. 262.
The parts of the same, displayed: _s_, Standard, or Vexillum; _w_,
Wings, or Alae; _k_, Keel, or Carina.]
263. =Irregular Flowers= may be polypetalous, or nearly so, as in the
papilionaceous corolla; but most of them are irregular through
coalescence, which often much disguises the numerical symmetry also. As
affecting the corolla the following forms have received particular
names:
264. =Papilionaceous Corolla=, Fig. 261, 262. This is polypetalous,
except that two of the petals cohere, usually but slightly. It belongs
only to the Leguminous or Pulse family. The name means butterfly-like;
but the likeness is hardly obvious. The names of the five petals of the
_papilionaceous_ corolla are curiously incongruous. They are,
The STANDARD or _Banner_ (_Vexillum_), the large upper petal which is
external in the bud and wrapped around the others.
The WINGS (_Alae_), the pair of side petals, of quite different shape
from the standard.
The KEEL (_Carina_), the two lower and usually smallest petals; these
are lightly coalescent into a body which bears some likeness, not to the
keel, but to the prow of a boat; and this encloses the stamens and
pistil. A Pea-blossom is a typical example; the present illustration is
from a species of Locust, Robinia hispida.
265. =Labiate Corolla= (Fig. 256-258), which would more properly have
been called _Bilabiate_, that is, two-lipped. This is a common form of
gamopetalous corolla; and the calyx is often bilabiate also. These
flowers are all on the plan of five; and the irregularity in the corolla
is owing to unequal union of the petals as well as to diversity of form.
The two petals of the upper or posterior side of the flower unite with
each other higher up than with the lateral petals (in Fig. 256, quite to
the top), forming the _Upper lip_: the lateral and the lower similarly
unite to form the _Lower lip_. The single notch which is generally found
at the summit of the upper lip, and the two notches of the lower lip, or
in other words the two lobes of the upper and the three of the lower
lip, reveal the real composition. So also does the alternation of these
five parts with those of the calyx outside. When the calyx is also
bilabiate, as in the Sage, this alternation gives three lobes or sepals
to the upper and two to the lower lip. Two forms of the labiate corolla
have been designated, viz.:--
_Ringent_ or _Gaping_, when the orifice is wide open, as in Fig. 256.
_Personate_ or _Masked_, when a protuberance or intrusion of the base of
the lower lip (called a _Palate_) projects over or closes the orifice,
as in Snapdragon and Toad-Flax, Fig. 257, 258.
[Illustration: Fig. 263. Corolla of a purple Gerardia laid open, showing
the four stamens; the cross shows where the fifth stamen would be, if
present.]
[Illustration: Fig. 264. Corolla, laid open, and stamens of Pentstemon
grandiflorus, with a sterile filament in the place of the fifth stamen,
and representing it.]
[Illustration: Fig. 265. Corolla of Catalpa laid open, displaying two
good stamens and three abortive ones or vestiges.]
266. There are all gradations between labiate and regular corollas. In
those of Gerardia, of some species of Pentstemon, and of Catalpa (Fig.
263-265), the labiate character is slight, but is manifest on close
inspection. In almost all such flowers the plan of five, which is
obvious or ascertainable in the calyx and corolla, is obscured in the
stamens by the abortion or suppression of one or three of their number.
[Illustration: Fig. 266. Two flower-heads of Chiccory.]
[Illustration: Fig. 267. One of them half cut away, better showing some
of the flowers.]
267. =Ligulate Corolla.= The ligulate or _Strap-shaped_ corolla mainly
belongs to the family of Compositae, in which numerous small flowers are
gathered into a head, within an involucre that imitates a calyx. It is
best exemplified in the Dandelion and in Chiccory (Fig. 266). Each one
of these straps or _Ligules_, looking like so many petals, is the
corolla of a distinct flower: the base is a short tube, which opens out
into the ligule: the five minute teeth at the end indicate the number of
constituent petals. So this is a kind of gamopetalous corolla, which is
open along one side nearly to the base, and outspread. The nature of
such a corolla (and of the stamens also, to be explained in the next
section) is illustrated by the flower of a Lobelia, Fig. 285.
[Illustration: Fig. 268. Head of flowers of a Coreopsis, divided
lengthwise.]
268. In Asters, Daisies, Sunflower, Coreopsis (Fig. 268), and the like,
only the marginal (or _Ray_) corollas are ligulate; the rest (those of
the _Disk_) are regularly gamopetalous, tubular, and five-lobed at
summit; but they are small and individually inconspicuous, only the
_ray-flowers_ making a show. In fact, those of Coreopsis and of
Sunflower are simply for show, these ray-flowers being not only sterile,
but _neutral_, that is, having neither stamens nor pistil. But in
Asters, Daisies, Golden-rods, and the like, these ray-flowers are
pistillate and fertile, serving therefore for seed-bearing as well as
for show. Let it not be supposed that the show is useless. See Section
XIII.
[Illustration: Fig. 269. A slice of the preceding more enlarged, with
one tubular perfect flower (_a_) left standing on the receptacle, with
its bractlet or chaff (_b_), one ligulate and neutral ray-flower (_cc_)
and part of another; _dd_, section of bracts or leaves of the
involucre.]
269. =Adnation, or Consolidation=, is the union of the members of parts
belonging to different circles of the flower (256). It is of course
understood that in this (as likewise in coalescence) the parts are not
formed and then conjoined, but are produced in union. They are born
united, as the term _adnate_ implies. To illustrate this kind of union,
take the accompanying series of flowers (Fig. 270-274), shown in
vertical section. In the first, Fig. 270, Flax-flower, there is no
adnation; sepals, petals, and stamens, are _free_ as well as distinct,
being separately borne on the receptacle, one circle within or above the
next; only the five pistils have their ovaries coalescent. In Fig. 271,
a Cherry-flower, the petals and stamens are borne on the throat of the
calyx-tube; that is, the sepals are coalescent into a cup, and the
petals and stamens are adnate to the inner face of this; in other
words, the sepals, petals, and stamens are all consolidated up to a
certain height. In Fig. 272, a Purslane-flower, the same parts are
adnate to or consolidated with the ovary up to its middle. In Fig. 273,
a Hawthorn-flower, the consolidation has extended over the whole ovary;
and petals and stamens are adnate to the calyx still further. In Fig.
274, a Cranberry-blossom, it is the same except that all the parts are
free at the same height; all seem to arise from the top of the ovary.
270. In botanical description, to express tersely such differences in
the relation of these organs to the pistil, they are said to be
_Hypogynous_ (i. e. under the pistil) when they are all _free_, that is,
not adnate to pistil nor connate with each other, as in Fig. 270.
[Illustration: Fig. 270. Flax-flower in section; the parts all
free,--hypogynous.]
_Perigynous_ (around the pistil) when connate with each other, that is,
when petals and stamens are _inserted_ or borne on the calyx, whether as
in Cherry-flowers (Fig. 271) they are free from the pistil, or as in
Purslane and Hawthorn (Fig. 272, 273) they are also adnate below to the
ovary.
[Illustration: Fig. 271. Cherry-flower in section; petals and stamens
adnate to tube of calyx,--perigynous.]
[Illustration: Fig. 272. Purslane-flower in section; calyx, petals,
stamens, all adnate to lower half of ovary,--perigynous.]
_Epigynous_ (on the ovary) when so adnate that all these parts appear to
arise from the very summit of the ovary, as in Fig. 274. The last two
terms are not very definitely distinguished.
271. Another and a simpler form of expression is to describe parts of
the flower as being
_Free_, when not united with or _inserted_ upon other parts.
_Distinct_, when parts of the same kind are not united. This term is the
counterpart of coalescent, as free is the counterpart of adnate. Many
writers use the term "free" indiscriminately for both; but it is better
to distinguish them.
_Connate_ is a term common for either not free or not distinct, that
is, for parts united congenitally, whether of same or of different
kinds.
_Adnate_, as properly used, relates to the union of dissimilar parts.
272. In still another form of expression, the terms superior and
inferior have been much used in the sense of above and below.
_Superior_ is said of the ovary of Flax-flower, Cherry, etc., because
above the other parts; it is equivalent to "ovary free." Or it is said
of the calyx, etc., when above the ovary, as in Fig. 273-275.
_Inferior_, when applied to the ovary, means the same as "calyx adnate;"
when applied to the floral envelopes, it means that they are free.
[Illustration: Fig. 273. Hawthorn-blossom in section; parts adnate to
whole face of ovary, and with each other beyond; another grade of
perigynous.]
[Illustration: Fig. 274. Cranberry-blossom in section; parts epigynous.]
273. =Position of Flower or of its Parts.= The terms superior and
inferior, or upper and lower, are also used to indicate the relative
position of the parts of a flower in reference to the axis of
inflorescence. An axillary flower stands between the bract or leaf which
subtends it and the axis or stem which bears this bract or leaf. This is
represented in sectional diagrams (as in Fig. 275, 276) by a transverse
line for the bract, and a small circle for the axis of inflorescence.
Now the side of the blossom which faces the bract is the
_Anterior_, or _Inferior_, or _Lower_ side; while the side next the axis
is the
_Posterior_, or _Superior_, or _Upper_ side of the flower.
[Illustration: Fig. 275. Diagram of papilionaceous flower (Robinia, Fig.
261), with bract below; axis of inflorescence above.]
[Illustration: Fig. 276. Diagram of Violet-flower; showing the relation
of parts to bract and axis.]
274. So, in the labiate corolla (Fig. 256-258), the li
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