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.]