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.]

[Illustratio