l8o BIOLOGICAL LECTURES. 



were in mind at the start. It suggests more than the mere 

 adaptation of the sporophyll to the form and function of the 

 vegetative leaf, directed by some influence which tends at the 

 time to force that function on it. It suggests that in general 

 vegetative leaves may have been derived from sporophylls. 



In other words, these results lend force to the proposition 

 offered by Bower (Ann. Bot., VIII, pp. 343-365, 1894) that the 

 sporophylls are primary organs, the vegetative leaves secondary 

 ones, and that sporophylls never have been derived from foliage 

 shoots, but that the converse is true. 



Aside from the questions of homology and phylogeny of foli- 

 age shoots and sporophylls, another one presents itself, which 

 suggests that one of the potent influences in the evolution of 

 vegetative organs on the sporophyte was a disturbance of the 

 carbon assimilatory function of the gametophyte in the gradual 

 passage of plants from an aquatic to a terrestrial life. This is 

 a purely theoretical consideration, and probably must always 

 remain so, though it is quite probable that artificial injury to the 

 gametophyte could be made to result in the sterilization of 

 sporogenous tissue, which was the first step toward the evolu- 

 tion of sporophytic vegetative organs. However, considering 

 the sporophyte alone, we have seen how artificial injury can be 

 made to influence the advance of a sporophyll to a foliage shoot 

 within a single life cycle, a demonstration of phylogeny in 

 ontogeny. 



