NATURE OF PLANTS 131 



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 off- 

 spring. You have already noted, page 52, that granular bodies 

 or chromosomes are constant features of every nucleus. It has 

 been supposed that these complex bodies direct the vital activi- 

 ties of the cell and determine the type of plant that shall be 

 developed. In other words the chromosomes contain or are 

 associated with the hereditary substances that cause each plant 

 to develop in a certain definite way or to follow a certain pattern 

 in its growth. The chromosomes derived from the parent plants 

 cause the offspring 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 they have been derived directly from the parent plant 

 by cell division. The gametes derived from the germinating spores 

 must also contain the same kind of hereditary substances as the 

 parent plants. In fertilization we have the fusion of the gametes. 

 This means that the hereditary substances in the gametospore 

 will be of a dual character since it has been derived from the 



