196 Minnesota Plant Life. 



and leaving them at the edge of the egg just inside its wall. 

 The remainder of the sperm-nucleus finds its way to the centre 

 of the female cell. In higher forms of naked-seeded plants, of 

 which the yews and pines are examples, the swimming-lashes 

 of the spermatozoids seem to have been quite abandoned. They 

 are indeed no longer necessary, for the old algal type of aquatic 

 reproduction has been finally outgrown. It is a most remark- 

 able and impressive fact that in all the terrestrial forms, from 

 the liverworts up to the cycads, including all the ferns, club- 

 mosses and their allies, the primitive aquatic nature of the plant 

 reasserts itself during the reproductive phase and one finds such 

 plants as the granite-mosses, accustomed to life upon bare, dry 

 rocks, quite unable to bring their sperms and eggs together 

 except immediately after heavy rains, when the surface of the 

 rock is flooded with water, thus enabling the aquatic sperms to 

 use their swimming threads. This long persistence, ages after 

 the aquatic habitat had been abandoned by the ancestral algae 

 from which the higher plants are supposed to have arisen, is a 

 striking example of the really profound inertia of living struc- 

 tures. 



