Evolution of the Basidiomycetes and Its Relation to the Terminology of the Basidium

SUMMARY

By excluding exceptional and isolated forms of the Basidiomycetes, it is possible to observe that there has been a general trend that has led from the Uredinales to the higher groups of the Basidiomycetes. This evolution has resulted from changes in life-cycles, from changes in time and position of nuclear divisions, and from changes in mode of living. It is possible to postulate that these variations have, to a great extent, resulted during geologic ages from slight differences in genetic characters that have been selected and perhaps continuously modified by environmental factors. As a result we are today dealing with forms, some of which have kept several primitive characters, but at the same time show others that are more advanced.

During the course of evolution of the Basidiomycetes, the haploid phase has become less and less important while the dikaryon stage has become dominant, and with this change, the process of spermatization has given way to plasmogamy. The basidium, once established, is essentially the same throughout the class but has undergone simplification as the result of loss of septation. Also, this same structure in the higher forms has taken over the functions of the probasidium so that it has become the locus of both caryogamy and meiosis. Because of the relatively gradual changes, and because of the essential unity in structure and function of this organ, the terminology relative to the basidium can be greatly reduced and a return may be made to the simple descriptive terms that were in vogue prior to the present age of ultra-refinement of definitions.