IOWA ACADEMY OF SCIENCES 
70 
it is I)y no means easy to know a lichen generation, while the stimulus and 
the tendency to vary imparted by fertilization doubtless extends wholly 
or largely to the fungal symbiont only. Surely the statistical and 
experimental methods of study of the origin of species may he regarded 
as a problem within the grasp of mycologists. 
Finally, this paper is not to be regarded as anything more than 
a brief, preliminary setting-forth of some problems which the writer h<^ 
in mind for future study. 
