126 



GROWTH OF THE CASTOR BEAN 



of the bean. The hilum and micropyle are more or less con- 

 cealed by a fleshy outgrowth, the caruncle (Fig. 85, ^). Remov- 

 ing the hard integument we find within a white, oily mass of 

 cells which are attached to the horn-like coat only at the hilum. 

 Cutting across this mass of cells it will be seen that two thin 

 leaves are imbedded in the center. Taking two other seeds and 

 cutting them longitudinally, one at right angles and the other par- 



Fig. 85. Seed and seedling of the castor bean: A, the seed with fleshy 

 outgrowth, the caruncle, c, at base. B, section of seed. At right showing 

 the two cotyledons, c, and short hypocotyl in center of the endosperm, en. 

 At left the seed is split parallel to the surface of the delicate white cotyledon. 

 C, early stage in the growth of the seedling. The hard integument is being 

 thrown off but the cotyledons are still entirely buried in the endosperm. D, 

 later stage. The cotyledons, c, still absorbing food from the endosperm, en, 

 are beginning to appear and to develop chlorophyll. K, the cotyledons and 

 plumule are expanding, the endosperm being entirely absorbed. 



allel to the leaves we see that the embryo consists of a very small 

 stem and root and two delicate leaves imbedded in an oily tissue, 

 the endosperm (Fig. 85, B). In the bean the seed consisted of 

 an embryo and integument. In the castor bean, the endosperm 

 forms the bulk of the seed, since it has been only partially con- 

 sumed by the embryo. It would naturally be inferred that the 



