4 6 



SEX AND HEREDITY 



sac, and one of the two gametes entering the ovum, its 

 nucleus may be seen to fuse with that of the ovum (Fig. 

 28). The result of fusion of the non-motile male gamete 

 with the non-motile ovum is the zygote, and from this 

 the embryo of a new plant develops. Here then is a 

 syngamy in which neither gamete is capable of independent 

 movement so as to secure the fusion. The opportunity 

 for movement in water, after the ancestral fashion of the 



FIG. 28. 



Fusion of male and female gametes of Lily (after Mottier). A, shows the 

 vermiform male nucleus applied to the egg-nucleus (Lilium Martagon) ; B, shows 

 the egg-cell of Lilium candidum with the two sexual nuclei fusing. The nuclear 

 membranes have disappeared at the place of contact. 



Ferns, is absent in accordance with the Land-Habit. The 

 fact that the flower is as a rule borne distally on the shoot, 

 and blooms habitually in bright sunny weather, precludes 

 the means of transit through water. In the course of 

 the Evolution of Seed Plants a new means of transit has 

 been substituted for it, better suited to their life on 

 Land. But the wonderfully adaptive growth of the 

 pollen-tube is in itself no more striking a phenomenon 

 than is the adaptive movement of the active sperma- 

 tozoid that it replaced. That it did replace it, and that 



