FERTILIZATION, EMBRYO, ENDOSPERM 339 



into the female gametophyte inside the ovule of a Flower- 

 ing Plant, one fuses with the egg to fertilize it, and the 

 other unites with the primary endosperm nucleus. From 

 the fertilized egg develops the young embryo sporophyte 

 plant. The endosperm nucleus now consists of three 

 fused nuclei and the process by which it is formed is often 

 referred to as " triple fusion. " It is sometimes called 

 " double fertilization " on account of the fact that one of 

 the cells taking part is a sperm. It grows and divides to 



Fig. 92. — Male gametophyte or pollen grain at time it is shed 

 from anther, (t) tube nucleus; (s) sperm mother cell which will divide 

 to form the two sperms. 



produce a special and peculiar tissue called endosperm. 

 In some seeds there is very little development of 

 endosperm while in others, like corn, there is a large de- 

 velopment so that the larger part of the mature seed con- 

 sists of endosperm. 



The Seed is the matured ovule containing a young 

 plant and a store of food (Fig. 94). The embryo plant has 

 been derived by cell division, growth, and differentiation 



