V] POLLINATION AND FERTILISATION 79 



The importance of the step thus taken is very 

 great. The most convincing indication of it is seen 

 in the numerical richness of the types which have 

 been emancipated from the restrictions imposed upon 

 Land-growing plants by fertilisation through the 

 medium of water. They exceed all other Vascular 

 plants both in number of species and of individuals, 



^^ • 



Fig. 17. Zamia tJoridana. Mature free-swimming spermatozoid, or 

 male gamete. ( x 150.) (From Strasburger, after H. J. Webber.) 



and form the dominating Flora of the present day. 

 On the other hand, the Cycads and Ginlgo show 

 all the signs of being archaic types. For the Cycads 

 are now represented by few genera, and are almost 

 confined to the Tropics, though formerly more Avidely 

 distributed ; while Ginlgo, which in earlier geological 

 periods was a relatively prevalent type, exists now 



