The boletes of Michigan, by Alexander H. Smith and Harry D. Thiers.

INTRODUCTION 25
of characters as presented by our present species concepts as representing a "hybrid swarm" situation, even though hybridization has not been
proven in laboratory studies. It would be curious indeed if the higher
fungi did not hybridize. Certainly, the field evidence in Leccinum, for
instance, indicates this. As cytological and genetical studies progress we
may even find the classification we have proposed here is too radical
rather than too conservative.