SEEDS AND SEEDLINGS 



119 



of the cotyledons. The cotyledons spread apart exposing the 

 growing plumule. The cotyledons may develop a green color 

 for a short time, but the food is gi'adually withdra-wn from them 

 to feed the young plant and they finally shrivel and fall away 

 (Fig. 84). The root system is permanent and develops 

 very rapidly. 



The Castor-Oil Bean Type. — This is a dicotyledonous seed 

 in which the food is stored in the endosperm (see page 98), sur- 



FiQ. 84. — Bean seedling coining through the soil. 



rounding the embryo-. The examination of the outside of the 

 seed shows the hilum at one end surrounded by the caruncle, 

 which serves for the passage of water to the inside. Upon the 

 removal of the seed coats we find a compact mass of white, mealy, 

 oily substance which is the endosperm. Between the seed coats 

 and the endosperm is a very thin papery covering, which is the 

 remnant of the nucleus (see page 96). Within the endosperm 

 we find the. embryo with its lai'ge but very delicate leaf-like 

 cotyledons (Fig. 85). It will be readily seen that in this type 

 of seed the embryo is relatively smaller than in the bean type 



