ell bulges at
one side, and this bulge becomes larger until it is nipped off from the
parent by contraction at the point of junction, and is then an
independent plant.

Next, there is the process by which one plant becomes two by the dying
off of some connecting portion between two growing parts.

Take, for instance, the case of the liverworts. In these there is a
thallus which starts from a central point and continually divides in a
forked or dichotomous manner. Now, if the central portion dies away, it
is obvious that there will be as many plants as there were forkings, and
the further the dying of the old end proceeds, the more young plants
will there be.

Take again, among higher plants, the cases of suckers, runners, stolons,
offsets, etc. Here, by a process of growth but little removed from the
normal, portions of stems develop adventitious roots, and by the dying
away of the connecting links may become independent plants.

Still another vegetative method of reproduction is that by bulbils or
gemmae.

A bulbil is a bud which becomes an independent plant before it commences
to elongate; it is generally fleshy, somewhat after the manner of a
bulb, hence its name. Examples occur in the axillary buds of _Lilium
bulbiferum_, in some _Alliums_, etc.

The gemma is found most frequently in the liverworts and mosses, and is
highly characteristic of these plants, in which indeed vegetative
reproduction maybe said to reach its fullest and most varied extent.

Gemmae are here formed in a sort of flat cup, by division of superficial
cells of the thallus or of the stem, and they consist when mature of
flattened masses of cells, which lie loose in the cup, so that wind or
wet will carry them away on to soil or rock, when, either by direct
growth from apical cells, as with those of the liverworts, or with
previous emission of thread-like cells forming a "protonema," in the
case of the mosses, the young plant is produced from them.

The lichens have a very peculiar method of gemmation. The lichen-thallus
is composed of chains or groups of round chlorophyl-containing cells,
called "gonidia," and masses of interwoven rows of elongated cells which
constitute the hyphae. Under certain conditions single cells of the
gonidia become surrounded with a dense felt of hyphae, these accumulate
in numbers below the surface of the thallus, until at last they break
out, are blown or washed away, and start germination by ordinary cell
d