g 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; wh