218 



SCHOOL AND HOME GARDENS 



cotyledons, which contain veins. When the castor bean 

 germinates, the hypocotyl forms a loop that pulls up 

 the cotyledons inclosed by the endosperm. The hard 

 testa gradually slips off, and the endosperm is absorbed 

 until nothing but a thin film remains. The cotyledons 



grow to form green 

 leaves, which serve 

 the plant as foliage 

 for some time. 

 Plant several rows of 

 castor beans in a box. After 

 the fifth day, take up one 

 row every third day and 

 study the development of 

 the parts. Leave some of the 

 plants in the box until the 

 cotyledons drop off. 



Note that the plumule 

 does not develop so rapidly 

 in the castor bean as in the 

 bean and that the cotyledons 

 grow until they become of considerable size, while those 

 of" the bean soon shrivel up and drop off. 



Germination of a grain of corn. When a grain of corn 

 germinates, the primary root, or the radicle, grows 

 toward the narrow end of the grain and breaks out of 

 its sheath near the hilum ; the plumule makes its appear- 

 ance at the opposite end. The young plant obtains 

 some food from the cotyledon, but the greater part of 



FIG. 121. The Castor-Bean Plant 



At the left the cotyledons are held 

 together by the endosperm 



