of Red
Maple; the seed-bearing portion cut open to show the seed. 15. Seed
enlarged, and divided to show the crumpled embryo which fills it. 16.
Embryo taken out and partly opened. 17. Embryo which has unfolded in
early stage of germination and begun to grow. 18. Seedling with next
joint of stem and leaves apparent; and 19 with these parts full-grown,
and bud at apex for further growth. 20. Seedling with another joint of
stem and pair of leaves.]

23. So, even in plants so much alike as Maples, there is considerable
difference in the amount of food stored up in the cotyledons by which
the growth is to be made; and there are corresponding differences in the
germination. The larger the supply to draw upon, the stronger the
growth, and the quicker the formation of root below and of stem and
leaves above. This deposit of food thickens the cotyledons, and renders
them less and less leaf-like in proportion to its amount.

[Illustration: Fig. 21. Fruit (one key) of Silver Maple, Acer
dasycarpum, of natural size, the seed-bearing portion divided to show
the seed. 22. Embryo of the seed taken out. 23. Same opened out, to show
the thick cotyledons and the little plumule or bud between them. 24.
Germination of Silver Maple, natural size; merely the base of the fruit,
containing the seed, is shown. 25. Embryo of same, taken out of the
husk; upper part of growing stem cut off, for want of room.]

24. =Examples of Embryos with thickened Cotyledons.= In the Pumpkin and
Squash (Fig. 26, 27), the cotyledons are well supplied with nourishing
matter, as their sweet taste demonstrates. Still, they are flat and not
very thick. In germination this store is promptly utilized in the
development of the caulicle to twenty or thirty times its length in the
seed, and to corresponding thickness, in the formation of a cluster of
roots at its lower end, and the early production of the incipient
plumule; also in their own growth into efficient green leaves. The case
of our common Bean (Phaseolus vulgaris, Fig. 28-30) is nearly the same,
except that the cotyledons are much more gorged; so that, although
carried up into the air and light upon the lengthening caulicle, and
there acquiring a green color, they never expand into useful leaves.
Instead of this, they nourish into rapid growth the plumule, which is
plainly visible in the seed, as a pair of incipient leaves; and these
form the first actual foliage.

25. Very similar is the germination of t