The title of this discussion is perhaps somewhat misleading i r i so f a r as the discussion d l cover primarily some recent work which does iiot deal too directly with the effects of radiation on fungi, but is concerned rather with chemically-induced mutations for nutritional deficiencies in NeTtrosyor-0. However, some justification exists for this approach.
In the first place, in Neurosporu, as in many other fungi, a large variety of types of miitational changes result from irradiation. These other fungi include Penicilliwm, Asperyilltcs, Trichophyton, Absidia, aptd Ophiostoma. An analysis of molephoiogicuh types of mutations at the biochemical level is rather difficult if not impossible a t present. As a consequencej f o r a critical evaluation of the effects of radiation, one might best consider only mutations of the somewhat simpler nutritional deficiency types. In these, as has been shown in many specific instances, the mutational eflcct can be traced to its action upon a particular biochemical reaction, presumably enzymatic. It is possible, therefore, that at this level we can detect arid analyze any differ*ential activities in the effects of radiations such as x-rays, neutrons, ultraviolet light, and others, as qualitative rather than quantitative differences. This might not he possible d i e n dealing wit11 mutations of less readily anal types.