at the end of summer, and germinate
in early spring. The embryo fills the whole seed, in which it is nicely
packed; and the nature of the parts is obvious even before growth
begins. There is a stemlet (caulicle) and a pair of long and narrow
seed-leaves (cotyledons), doubled up and coiled, green even in the seed,
and in germination at once unfolding into the first pair of
foliage-leaves, though of shape quite unlike those that follow.

21. Red Maple seeds are ripe and ready to germinate at the beginning of
summer, and are therefore more convenient for study. The cotyledons are
crumpled in the seed, and not easy to straighten out until they unfold
themselves in germination. The story of their development into the
seedling is told by the accompanying Fig. 14-20; and that of Sugar Maple
is closely similar. No plumule or bud appears in the embryo of these two
Maples until the seed-leaves have nearly attained their full growth and
are acting as foliage-leaves, and until a root is formed below. There is
no great store of nourishment in these thin cotyledons; so further
growth has to wait until the root and seed-leaves have collected and
elaborated sufficient material for the formation of the second internode
and its pair of leaves, which lending their help the third pair is more
promptly produced, and so on.

22. Some change in the plan comes with the Silver or Soft White Maple.
(Fig. 21-25). This blossoms in earliest spring, and it drops its large
and ripened keys only a few weeks later. Its cotyledons have not at all
the appearance of leaves; they are short and broad, and (as there is no
room to be saved by folding) they are straight, except a small fold at
the top,--a vestige of the habit of Maples in general. Their unusual
thickness is due to the large store of nutritive matter they contain,
and this prevents their developing into actual leaves. Correspondingly,
their caulicle does not lengthen to elevate them above the surface of
the soil; the growth below the cotyledons is nearly all of root. It is
the little plumule or bud between them which makes the upward growth,
and which, being well fed by the cotyledons, rapidly develops the next
pair of leaves and raises them upon a long internode, and so on. The
cotyledons all the while remain below, in the husk of the fruit and
seed, and perish when they have yielded up the store of food which they
contained.

[Illustration: Fig. 14. One of the pair of keys or winged fruits