NATURE OF PLANTS 



123 



nate and produce a plant. The microspores and megaspores, 

 however, were not formed by the union of sexual cells or gametes. 

 Therefore we may distinguish them as asexual spores or simply 

 spores. It has frequently been observed that the endosperm 

 nucleus also attracts the other male gamete and causes a similar 

 fusion with it (Fig. 80). The union of the male and female 



FIG. 80. The micropylar end of an ovule of Canada lily (sectional view), 

 showing the process of fertilization or fecundation. The tube, /, has grown 

 into the female gametophyte and ruptured, discharging the two male gametes. 

 One, d" , is seen fusing with the female gamete, 9 , and the other one, d" 1 ', is 

 uniting with the two polar cells, thus forming the endosperm nucleus; s, one 

 of the synergids; i, integuments. 



gametes is called fertilization or fecundation. Unless fertilization 

 is effected the growth outlined above usually ends the history of 

 the flower. But if fecundation is effected then a gametospore 

 is formed that is capable of germinating and producing a plant 

 whose growth and development are attained with most remark- 

 able changes of the ovule and often of the surrounding parts. 

 54. The Germination of the Gametospore and the Formation 

 of Seed. The first indication of the germination and growth of 

 the gametospore is seen directly after fertilization. It becomes 



