206 



Science of Plant Life 



or male cell, with the egg, or female cell, is the act oj 

 fertilization. 



The fertilized egg immediately begins to develop ; that is, it 

 grows and divides into a large number of cells, and from it 

 eventually comes the embryo or young plant that is found 

 within the seed. Fertilization is the essential part of sexual 

 reproduction both in plants and animals, and it marks the 

 actual beginning of a new generation. After the egg is fer- 

 tilized, it is able to develop into a new plant or animal of the 

 same kind as its parents. It should be understood that the 

 sperms from one pollen tube fertilize the egg in only one ovule, 

 and that to fertilize all the eggs, as many pollen tubes must 



FIG. 123. Diagram to illustrate stages in the reproduction of a seed plant. A shows 

 pollen grains (b) from anther (a) on top of stigma ; B shows a stage in the growth of 

 the pollen tube and the formation of the egg cell ; C is the stage when the pollen tube 

 has reached the egg and sperm and egg unite; D shows the formation of the embryo 

 plant within the seed; and E shows the further development of the embryo and the 

 maturing of the seed coats. The young plant thus formed and incased may remain 

 alive for years within the seed. 



