PLANT WORLD CONTINUED 



Fig. 149. Diagram of Life-cycle of an Angiosperm (Alisma 



Plantagoaquatica) . 



9, female gametophyte (embryo-sac) ; 8a and 9a, male gameto- 

 phyte (pollen-grain). (After J. H. Schaffner). 



Fig. 150. 



Development of the pea fruit from the pea flower. (After 

 Yung's Chart). 



tiny stem with a little root at one end and two rudimentary leaves at 

 the other. 



The gametophyte has, in the meantime, resumed its development 

 on account of the union of the second sperm nucleus with the two polar 

 nuclei to form the endosperm nucleus. This endosperm nucleus divides 

 rapidly, although the cell walls are much delayed in this development. 

 In a short time the endosperm has surrounded the embryo sporophyte 

 and has rilled in the growing ovule. This surrounding and nourishing 

 cell mass is now called the endosperm, which is neither gametophyte 

 nor sporophyte. 



As the ovule grows in size, its outer coat becomes thickened and 

 hardened, and the endosperm within has enlarged and solidified. A 

 layer of cells at the base of the ovule now becomes corky and checks 



