124 NATURE OF FERTILIZATION 



one or more (4) sexual cells or gametes. These two phases are 

 called respectively the sporophyte or asexual generation, and the 

 gametophyte or sexual generation, since in the first phase mother 

 cells are developed which form spores, i. e., this is the spore 

 forming or asexual generation and in the second phase gametes 

 or sexual cells are produced. 



58. Significance of Fertilization. Let us now stop to con- 

 sider the meaning of the complicated process that we have termed 

 fertilization. No satisfying explanation has been offered. Some 

 see in these changes only a process of nutrition and chemical 

 stimulation. The gametes are lacking in certain materials that 

 are essential to their further growth. According to this view 

 the male gamete is the complement of the female and by the 

 union of the two all the substances are supplied that are neces- 

 sary for growth. 



It has also been suggested that the growth culminating in 

 fertilization is attended with the removal of impurities from the 

 sexual cells. Every cell has its growth, maturity, and senescence 

 when it loses its power for further growth and division. The 

 reduction division and the subsequent formation of the gametes 

 results in the removal of substances that prevent their continued 

 activity and as a consequence they are restored to a youthful 

 condition which appears in the growth of the gametospore. 



Much attention has been directed in recent years to the process 

 of fertilization as a method of controlling the character of 

 of offspring. You have already noted, page 49, that granular 

 bodies or chromosomes are constant features of every nucleus. 

 It has been supposed that these complex bodies direct the vital 

 activities of the cell and determine the type of plant that shall 

 be developed. In other words the chromosomes contain the 

 hereditary substances that cause each plant to develop in a cer- 

 tain definite way or to follow a certain pattern in its growth. 

 The chromosomes derived from the parent plants cause the off- 

 spring to resemble them in growth. The micro- and mega-spores 

 are formed in the sporophylls, and these spores must therefore 

 contain the same kind of chromosomes or hereditary substances 

 as the plants bearing the sporophylls, i. e. } the parent plant, since 



