Fig. 8.—Three stages in the growth of a Sycamore Seedling. cot., cotyledons; fol., first pair of foliage leaves. (Slightly reduced.) [Pg 15] The germinating vegetable-marrow seed possesses a curious contrivance for pulling its cotyledons out of the seed-coat. This is a peg (p, Fig. 10) which develops at the top of the radicle, and holds down the lower half of the seed-coat whilst the other half is forced upwards to allow the cotyledons to be withdrawn. Fig. 9.—Three stages in the growth of the Yellow Lupine. On the right the cotyledons are still enclosed in the mottled seed-coat. In the middle plant the cotyledons are spreading out; the first foliage leaves have not yet unfolded. On the left, the first two foliage leaves are unfolding, and the cotyledons have spread out flat. (Slightly reduced.) After a little thought a possible explanation of these differences in the cotyledons suggests itself. It may be that, in the case of the mustard and sycamore, leaves are required as early as possible, while the bean and pea have no immediate need for leaves because their cotyledons contain so much stored food. The cotyledons of these plants shrivel up as the seedling grows, and this seems to indicate that [Pg 16] during its early stages the plant lives upon this food. In Chapter II. we shall make experiments to see if this explanation is the true one. If so, the lupine and vegetable-marrow seeds evidently rely partly upon their stored food and partly upon setting the cotyledons to work as leaves, whilst the plant is still very young. Fig. 10.—Germinating Vegetable Marrow seed. p, the peg by which the seed-coat (s.c.) is held down to allow the cotyledons (cot.) to be withdrawn. (× 1.) (After Bailey.) Fig. 11.—A germinating Pea; cot, cotyledon; pl, plumule; R, radicle; r.h., root-hairs; S.c., seed-coat. The radicle has been marked with Indian ink at intervals of 1/10”. The true leaves.—The cotyledons are really makeshift leaves, which are already formed in the seeds. Even when they expand and become green they do not live long, but as soon as the next few leaves are well established, shrivel up and wither. The true or “foliage” leaves first make their appearance as a bud which surrounds the growing point of the stem. As this part of the stem increases in length, the foliage leaves become separated from each other and spread out to the light and air.