THE AMERICAN NATURALIST [Vol. XLII 



Macho <• ran tli cm aspcra ~ M aclucranthcra riscosa as/, era: variant. 



In concluding, the ecologist will confess frankly that 

 he does not know what a species is. On the other hand, 

 he is certain that he knows some of the things it is not, 

 and that the species of the descriptive botanist comprise 

 several widely different things. Just what these are and 

 what their relation to species, if there are such, is a 

 matter to be decided by experiment alone. The ques- 

 tion of what a species is can not even be answered pro- 

 visionally until a sufficiently large number of experi- 

 ments have been made to indicate the regular procedure 



that control it. 



