EVOLUTION OF ANGIOSPERMS THROUGH APOSPORY 167 



young plants sexually, and these would then correspond com- 

 pletely, in their origin, with the embryo of a flowering plant. 

 The parallel with one of the Ncphrodium varieties is complete 

 in the genus Bj-yofhyllam where from certain points on the 

 margins of the leaves young plants can arise, and not merely 

 ovules which have to be fertilized, or pollen-grains to fertilize 

 them. In the genus Begonia the tissues of the leaves retain 

 still more of their cotyledonary functions and can produce 

 aposporous new plants with almost as much facility as in JVe^hro- 

 d 1 117)1. 



The more complete form of apospory, shown in JVephrodtujn, 

 BryofhyUtim and Begonia^ not only omits the spores, but also 

 passes by the stage in which new conjugations can be under- 

 taken. It becomes simply a method of vegetative propagation. 

 As such it may have an environmental advantage, but it con- 

 stitutes at the same time a grave evolutionary danger. Habitual 

 vegetative propagation conduces to deterioration of sexual proc- 

 esses and final sterility. The more advantageous purely vege- 

 tative forms of aposporous propagation might become, the more 

 certain would be the extinction of the species. 



In proportion as plants rely upon vegetative propagation the 

 power of sexual reproduction declines. Many domesticated 

 and wild plants might be cited as representing stages in this 

 process of deterioration. That there are no wild angiosperms 

 in which the power of sexual reproduction is entirely lacking, 

 may be taken to indicate that organisms of this stage of devel- 

 opment can not long survive the discontinuance of sexual repro- 

 duction. 



It would appear, then, that the form of apospory which could 

 open the way to the evolution of angiosperms must have been 

 radical enough to eliminate the macrospores and attach the 

 aposporous prothallus to the parent plant, but not great enough 

 to exclude the formation of egg-cells and the continuation of 

 sexual reproduction. 



ANTICIPATION INSTEAD OF RECAPITULATION. 



The currently accepted doctrine or "biogenetic law" of re- 

 capitulation tends to conceal the possibility of such evolutionary 



