196 Minnesota Plant Life. 



and leavinj:^' them at the edi^e of tlie egg^ just inside its wall. 

 The remainder of the sj-jerm-nncleus finds its way to the centre 

 of the female cell. Tn higher forms of naked-seeded ])]ants. of 

 which the yews and pines are exami)les, the swimming-lashes 

 of the spermatozoids seem to have heen qnite abandoned. Thev 

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

 reproduction has heen finallN- outgrown. Tt 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 priniiii\e a(|uatic natiu-e of the plant 

 reasserts itself during the rejjroductive phase and one finds such 

 ])lants as the granite-mosses, accustomed to life upon l)are, dry 

 rocks, quite unable to bring their sperms and eggs together 

 excei)t innnediately after hea\y 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 

 horn which the higher plants are supjjosed to have arisen, is a 

 striking example of the really profound inertia of living struc- 

 tures. 



