PLANTS MULTIPLY BY MEANS OF STEMS.
7. Two grasses in fierce contention.--In growing a lawn at the
Michigan Agricultural College, a little Bermuda grass was scattered
with June grass, and the struggle has been most interesting. In the
spring and for six weeks in autumn, when moisture usually abounds
and the weather is cool, June grass thrives and little else is seen.
In the dry, hot weeks of July and August, June grass rests and the
Bermuda, which continues to spread, assumes control of the lawn, with
but little of the June grass in sight. Each struggles for possession
and does the best it can, and to some extent one supplements the other,
with the result that at all times from spring to fall there is a close
mat of living green which delights the eye and is pleasant to the
feet that tread upon it. In soft ground, with plenty of room, a bit
of quick or quack grass, or Bermuda, will extend in a year three to
five feet or more in one direction.
[Illustration: FIG. 6.--Rootstock of quick grass which has grown
through a potato, and in this way may be carried to another field
or another farm.]
June grass, quick grass, Bermuda grass, redtop, and white clover,
wherever opportunity offers, spread by means of jointed stems,
creeping and rooting at every joint on the surface of the ground or
a little way below. These are not roots at all, but true stems somewhat
in disguise. Here may also be mentioned, as having similar habit,
artichokes, peppermint, spearmint, barberry, Indian hemp, bindweed,
toadflax, matrimony vine, bugle-weed, ostrich fern, eagle fern,
sensitive fern, coltsfoot, St. John'swort, sorrel, great willow-herb,
and many more.
8. Runners establish new colonies.--The spreading of strawberries
by runners must be familiar to every observer. In 1894 a student
reported that a wild strawberry plant in the botanic garden had
produced in that year 1230 plants. Weeds were all kept away, the season
was favorable, the soil sandy; but on one side, within a foot and
a half, progress was checked by the presence of a large plant of
another kind. The multiplication of this plant by seeds, in addition
to that by runners, would have covered a still greater area of land.
Other plants with runners much like the strawberry are: several kinds
of crowfoot, barren strawberry, cinquefoil, strawberry geranium, and
orange hawkweed. Plants of the star cucumber, one-seeded cucumber,
grapes, morning-glories, and others, spread more or less over bushes
or over the ground, and are thus enabled to scatter seeds in every
direction.
[Illustration: FIG. 7.--The runner of a strawberry plant.]
9. Branches lean over and root in the soil.--A black raspberry grows
fast in the ground and has to stay in one spot for life. It has neither
legs, feet, nor wings, and yet it can travel. The bush takes deep
root and spreads out its branches, which are sometimes ten feet or
more in length; the tips of these branches curve over to the ground
six feet away, and finally take root; from these roots new colonies
are formed, five to twenty in a year from one bush.
True, the old roots do not get far, and the new plants only get about
six feet in one season, but they have made some progress. This is
rather slow locomotion, you say; but let us look a little farther,
remembering that a seed is a little plant packed ready for
transportation. This second mode of spreading will be described on
a future page.
[Illustration: FIG. 8.--Plant of a black raspberry showing one branch
(stolon) with several tips rooting.]
10. Living branches snap off and are carried by water or wind.--Some
trees and shrubs among the willows are called snap-willows, because
their branches are very brittle; on the least strain from wind, rain,
sleet, or snow, the smaller branches snap off near the larger branches
or the main trunk, and fall to the ground. At first thought this
brittleness of the wood might seem to be a serious defect in the
structure of the tree or shrub, although they seem to produce branches
enough for their own use.
But the branches which are strewn all around after a storm often take
root in the low ground where they fall; some of them are carried down
stream by the current, and, lodging on the shore below, produce new
trees or bushes. During the winter of 1895 and 1896 a group of seven
white willows, near a brook on the campus of the Michigan Agricultural
College, was at one time loaded with sleet. There was considerable
snow on the ground, which, of course, was covered with an icy crust.
In a little while the sleet melted from the fallen branches strewn
about, and a moderate breeze then drifted the smallest of the twigs
in considerable numbers over the icy snow. Some of these were found
thirty rods distant from the parent trees--not down stream in the
valley of the brook, but up the stream. Had not the low ground been
covered with a dense growth of grass, some of these branches might
have started new trees where the wind had left them.[1]
[Footnote 1: C. D. Lippincott believes that this is a provision of
nature to dispose of the now unnecessary branchlets without leaving
a knot. _Plant World_, Vol. I, p. 96.]
[Illustration: FIG. 9.--Branch of snap-willow rooting at one end.]
The branches on slow-growing limbs of cottonwood and large-toothed
aspen are much enlarged at the nodes, and at these places are brittle,
often separating from the tree and breaking up into pieces. Under
a small cottonwood were picked up a bushel or more of such limbs,
all yet alive. These trees are common on low land, and, like
snap-willows, the severed twigs may find a chance to grow on moist
soil.[2]
[Footnote 2: The brittle branches of salix were noticed by the author
in _Bull. Torr. Bot. Club_, Vol. IX (1883), p. 89.]
[Illustration: FIG. 10.--Portion of a branch of the cottonwood as
it fell from the tree.]
In a greenhouse a potted plant of _Selaginella emiliana_(?) was
placed on the bench near the aisle, where it was often brushed by
people in passing. Small branches, not being firmly attached, were
frequently broken from the main plant and fell upon the moist sand,
where they rooted in abundance.