THE SPURGE FAMILY 



123 



2. The Seed and its Germination. — The seed has a hard and 

 mottled testa, which shows at its thinner end a whitish growth — 

 the caruncl4 — covering the micropyle. Break the testa and you 

 will find the seed enclosed in a second membranous cover, the 

 tegmen. Remove this as well, and look for the embryo: you 

 will find the end of the hypocotyl (radicle) at that end where 

 the micropyle and the caruncle were seen, and, above the hypo- 

 cotyl, the rest of the embryo, cotyledons and plumule, not bent 

 as in the Bean, but perfectly straight. Besides, the cotyledons 

 are not thick but papery, and surrounded by a white oily sub- 

 stance, the endosperm. 



Now, when we go to sow the seed and study its germination, 

 the first sign of the growing plant is a small hook, just as it was 



Fig. 114.— Seed of Castor-Oil plant. 



in the case of the Gram seed (page 31). This hook ends at one 

 side in a root, which soon fixes the plant in the soil, and at the 

 other side in the seed, in which the cotyledons remain buried for some 

 time. When they are drawn out, they are much larger and thicker 

 than before, have a green hue and often a slimy substance on their 

 lower sides. The testa is now empty and the endosperm is 

 vanished. What has happened is this: the cotyledons have 

 absorbed the fatty endosperm by their lower and outer side and, 

 at its expense, have developed the root, enlarged the hypocotyl 

 and also themselves; the plantlet is now established in the soil and 

 able to obtain its nourishment from the ground and the air by 

 ineans of its root and its green leaves. In a short time the 

 plumule also grows and develops stem and foliage-leaves, which, 

 however, differ considerably in shape from the seed-leaves. 



