HOW SHOULD THE INFERTILITY OF INTERSPECIES CROSSES BE DESIGNATED

Infertility is widely used in fungi as a criterion for distinguishing sibling species and mating populations. Whether a cross is called fertile or sterile may depend on the frame of reference. The terms are relative rather than absolute. Failure to recognize this had led to apparent contradictions where none exist. In many situations the unqualified terms are insufficiently precise and descriptive modifiers will be required, for example, ''highly or sparingly fertile, nearly or completely barren.'' Precision is also needed in describing the reduction in fertility that is characteristic of certain genotypes when crosses are made between individuals of the same species.