The seed of the yellow lupine.—The seed of the yellow lupine is about as large as a pea, but it is slightly flattened in shape. The seed-coat is prettily mottled; when it is removed, the greater part of the seed is found to consist of two cotyledons. They are somewhat swollen, but the stored food is not starch. The plumule and radicle occupy positions similar to those of the bean and pea. The vegetable marrow seed.—This seed has a rather curious shape, and somewhat resembles a pocket-flask. It is flattened, and the border of the seed-coat is thickened and of silky appearance, the rest of the “skin” having some resemblance to kid. The two cotyledons, which compose the greater part of the seed, are white and only slightly fleshy. The plumule and radicle are at the pointed end of the seed, and are difficult to see. The mustard seed.—In comparing the mustard seed with those [Pg 8] already described, one is struck with the great difference in size. An average broad-bean seed weighs about 600 times as much as the mustard seed. While the two fleshy cotyledons make up the bulk of the seed of the bean, pea, lupine and vegetable marrow, the cotyledons of the mustard seed are thin and leaf-like. They are folded on themselves, one inside the other (as at g, Fig. 61), and enclose the radicle. The characters of the cotyledons account very largely for the small size of the mustard seed. It will be seen, when the growth of the young plants is watched, that the difference is associated with the special duties which the cotyledons perform in the various cases. Fig. 4.—Sycamore Fruit, cut through in the plane of the wing. s.c., seed-coat (indicated by a thick, broken line); f.w., fruit-wall; h, layer of fine hairs; R, radicle; pl., plumule; cot. 1, cot. 2, cotyledons (diagrammatically shaded). (× 2.) The sycamore seed.—What is generally called the seed of the sycamore is really a fruit. The fruits are in pairs (Figs. 33 and 137), and each half consists of a flat wing and a rounded case in which the seed itself is enclosed. The round seed-cases of the two [Pg 9] fruits are connected together. When they come apart, a scar marks the place where they were formerly in contact, and a little cord runs out to each fruit from the stalk on which the pair of fruits is borne.