130 



NATURE OF THE SEED 



looser structure of the hilum. This can easily be demonstrated 

 by placing beans in water, when the spread of the water from the 

 region of the micropyle will be indicated by the swelling and 

 wrinkling of the integument (Fig. 83, C). After a time the 

 entire integument becomes quite soft and water is readily drawn 

 through it owing to the fact that the storage foods in the embryo 

 are in close contact with it and draw the water through by 

 osmosis. Carefully removing the integument from a soaked bean 



FIG. 83. Fruit and seed of the bean: A, mature fruit or pod: s, style; 

 c, remains of calyx; o, ovary. At left the pod has been opened, showing four 

 seeds attached to the walls of the ovary by funiculus. B, two views of a 

 seed h, hilum or scar marking attachment of funiculus to seed; m, micropyle. 

 C, wrinkling of seed coat caused by the entrance of water through the micro- 

 pyle and hilum. D, embryo of seed after removal of integument c, coty- 

 ledons. At right one of the cotyledons has been removed to show the plumule, 

 ep, and the hypocotyl, hy. E, half of the membranous integument. 



we note that the embryo is well developed, consisting of two 

 fleshy cotyledons and a short stem (Fig. 83, D, E). The plumule 

 is well developed, bearing two leaves, and the short hypocotyl 

 and root are enclosed in a sheath formed from the integument. 

 Note that the hypocotyl and root are situated near the micropyle. 

 How does this arrangement work to the advantage of the em- 

 bryo? Allow the seed to germinate and it will be noted that the 

 absorption of water first causes the embryo to expand and rupture 

 the integument. This is immediately followed by the growth and 

 elongation of the lower part of the hypocotyl which results in the 

 pushing out of the root (Fig. 84, A). Thus it happens that the 

 very part of the embryo that shows the first signs of growth is in 



