132 APPLIED BIOLOGY 



should be noted that the important point concerning fertiliza- 

 tion is that it is the union of two cells to start the development 

 of an embryo. 



The method of reproduction by generative cells or germ- 

 cells (sexual reproduction), which has been illustrated by the 

 frog and the bean plant, is the only method in a large number 

 of species of plants and animals ; but in both there are many 

 species which may at times reproduce without germ-cells. 

 Reproduction of certain plants from roots, stems, etc., will 

 be described in the next chapter ; and many lower animals 

 reproduce by automatically dividing themselves. Such re- 

 production of plants and animals without germ-cells is termed 

 asexual (i.e., independent of sex). 



