NATURE OF PLANTS 



109 



forming a single cell. This body is a sexually formed spore or 

 gametospore and like the ordinary spore has the power to germi- 

 nate and produce a plant. The microspores and megaspores, 



Fig. So. The micropylar end of an ovule of Canada lily (sectional view), 

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

 into the female gametophyte and ruptured, discharging the two male 

 gametes. One, c?, is seen fusing with the female gamete, ?, and the other 

 one, <$', is uniting with the two polar cells, thus forming the endosperm 

 nucleus ; s, one of the synergids ; i, integuments. 



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

 gametes. Therefore we may distinguish them as asexual spores 

 or simply as 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 gametes is called fertilization or fecundation. Unless 

 fertilization is effected the growth outlined above practically 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 remarkable changes of the ovule and often of the 

 surrounding parts. 



