NATURE OF PLANTS 



119 



is only after the food has been withdrawn that the shriveled 

 cotyledons drop off. As the young plant becomes established 

 the plumule unfolds like a bud and develops the stem and leaves 

 and finally the flowers and fruit with which you are familiar. 



The castor bean shows quite a variation from the structure 

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

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



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 cotyle- 

 don. 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. 

 E, the cotyledons and epicotyl are expanding, the endosperm being entirely 

 absorbed. 



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 



