THE WORK OF LEAVES 179 



ground of difference in function ? The Horse-bean seed- 

 leaves are very thick and gorged with food; those of 

 the Castor- bean are extremely thin and contain prac- 

 tically no food: on the contrary, the nutriment (en- 

 dosperm) is packed around them and it is their task 

 to absorb it. For this purpose they are closely and 

 firmly attached to it and are provided with veins 

 which help to convey the nutriment directly to the 

 germ. As soon as germination begins they enlarge, 

 and so increase their absorptive surface, and they 

 continue to absorb the nutriment long after they have 

 come above ground. When the food has entirely 

 disappeared the husk falls away, leaving the seed- 

 leaves free. 



The Corn has a seed-leaf (Fig. 6, I) which is both 

 a storehouse and an absorbing organ; it is the small 

 white, shield -shaped portion of the germ which is 

 closely applied to the starchy endosperm (the endo- 

 sperm is shaded in the figure) . If Sugar Corn can be 

 obtained, a drop of iodine will show that the endo- 

 sperm contains little or no starch, while the seed-leaf 

 is gorged with it. Remove the endosperm from ger- 

 minating plants of Corn and Castor -bean, and com- 

 pare their subsequent growth with that of uninjured 

 control plants. 



What other familiar seeds have endosperm and ab- 

 sorbent seed-leaves? Notice the curious seed-leaf of 

 the Cocoanut (Fig. 45), which consists of a soft. 



