v] POLLINATION AND FERTILISATION 77 



spermatozoids to the terrestrial method by a pollen- 

 tube ? A certain degree .of probability that such a 

 change had taken place was derived long ago from 

 the general comparison of the propagative methods 

 in Ferns and Flowering plants. But the demon- 

 stration of spermatozoids still surviving in some 



a 



Fig. 16. Zamia floridana. Distal end of the pollen-tube, showing 

 the vegetative prothallial cell (v), the sterile sister-cell (s) and the 

 two spermatozoids. a, before movement of the spermatozoids 

 has commenced ; &, after the beginning of ciliary motion : the 

 prothallial cell is broken down, and the separation of the two 

 spermatozoids is taking place. ( x circa 75.) (From Strasburger, 

 after H. J. Webber.) 



Seed-bearing plant would naturally appear more 

 conclusive than such comparisons could possibly be. 

 Some botanists had long been expectant that instances 

 of this would eventually be found. The expectation 

 has now been realised in the case of two ancient 



