e "endosperm." This fills up the whole seed which
is surrounded by the hardened shell derived from the integument and
wall of the ovule. The embryo is elongated with a circle of small
leaves at the end away from the opening of the ovule toward which is
directed the root of the embryo.

The seed may remain unchanged for months, or even years, without
losing its vitality, but if the proper conditions are provided, the
embryo will develop into a new plant. To follow the further growth of
the embryo, the ripe seeds should be planted in good soil and kept
moderately warm and moist. At the end of a week or two some of the
seeds will probably have sprouted. The seed absorbs water, and the
protoplasm of the embryo renews its activity, beginning to feed upon
the nourishing substances in the cells of the endosperm. The embryo
rapidly increases in length, and the root pushes out of the seed
growing rapidly downward and fastening itself in the soil (_G_, _r_).
Cutting the seed lengthwise we find that the leaves have increased
much in length and become green (one of the few cases where
chlorophyll is formed in the absence of light). As these leaves
(called "cotyledons" or seed leaves) increase in length, they
gradually withdraw from the seed whose contents they have exhausted,
and the young plant enters upon an independent existence.

The young plant has a circle of leaves, about six in number,
surrounding a bud which is the growing point of the stem, and in many
conifers persists as long as the stem grows (Fig. 75, _K_, _b_). A
cross-section of the young stem shows about six separate
fibro-vascular bundles arranged in a circle (_S_, _fb._). The root
shows a central fibro-vascular cylinder surrounded by a dark-colored
ground tissue. Growing from its surface are numerous root hairs
(Fig. 75, _M_).

For examining the microscopic structure of the pine, fresh material
is for most purposes to be preferred, but alcoholic material will
answer, and as the alcohol hardens the resin, it is for that reason
preferable.

Cross-sections of the leaf, when sufficiently magnified, show that
the outer colorless border of the section is composed of two parts:
the epidermis of a single row of regular cells with very thick outer
walls, and irregular groups of cells lying below them. These latter
have thick walls appearing silvery and clearer than the epidermal
cells. They vary a good deal, in some leaves being reduced to a
si