PARTS OF SEEDS: THE CASTOR BEAN 5 



endosperm,* which is covered by a thin papery material.! The 

 embryo lies within the endosperm; its radicle at the end next 

 the caruncle. The two cotyledons are thin and covered by the 

 endosperm. 



6. Germination of the castor bean. The spongy substance 

 of the caruncle becomes much swollen by absorption of water. 

 In germination the swelling of the embryo and endosperm by 

 the absorption of water bursts the rigid seed coat causing it to 

 crack lengthwise, so that a portion of the endosperm can be seen 

 through the crack. The radicle emerges from the end where the 

 caruncle is located. The hypocotyl, which is very short in the 

 embryo stage, now elongates. The seed being bulky is not readily 



Fig. 9- 

 Germination of castor-oil bean. 



pushed up through the soil. The hypocotyl part of the stem arches 

 upward forming a loop and as it elongates and endeavors to 

 straighten up it pulls the "seed-" from the ground. Figure 9 

 shows different stages. The hard seed coat gradually slips off. 

 The white endosperm is now very distinct and is seen to cover up 

 the cotyledons \vhich remain closed. It can be seen, however, 

 that the endosperm is " wasting away," that it is being absorbed 

 through the outer faces of the cotyledons. By this means, they are 

 exposed to the light and take on a green color. The mass of the 

 endosperm becomes less and less, until finally there is but a thin 



* The endosperm is food stored in the seed outside of the embryo. 

 f This papery lining is the dead remnant of the nucellus which was used 

 up in the growth of the endosperm. See Chapter XXXV. 



