A GENERAL SURVEY 23 



the other hand, they produced seeds somewhat 

 after the manner of the present-day cone- 

 bearing plants. The only living representatives 

 of these plants on the earth at the present time 

 are to be found in the tropical Cycads, plants 

 resembling palms in their general appearance, 

 though actually very distinct in all other ways. 

 One very singular point in connection with these 

 Cycads is that the act of fertilisation is carried 

 out by means of actively moving male cells, 

 exactly resembling the spermatozoids which are 

 so common amongst the fiowerless plants. 

 This is in direct contrast to the scheme of the 

 flowering plants as a whole, where the generative 

 cells are conveyed to the egg cell by the growth 

 of the process known as the pollen tube. 

 Although a pollen tube is formed in the Cycads, 

 this is only to start the spermatozoids on their 

 way ; the final stages of the journey are accom- 

 plished by their own activities. In one species 

 of Cycad [Cycas revohita) no attempt is made in 

 the female plant to produce cone or flower. The 

 carpels, or fruit-bearing organs, are developed on 

 singularly leaf-like processes which are strongly 

 suggestive of the spore-bearing fronds of the 

 ferns. The resulting seeds are large and of a 



