One of the problems of the investigator of parasitic fungi is that of obtaining ascospore stages of the organism in cultures derived from diseased plant parts. Such cultures often produce mycelium or mycelium and conidia without the corresponding ascospore stage. With the advent of our knowledge of heterothallism such sexual stages have often been grown artificially by the mating of self-sterile strains. A few cases of heterothallism, in which the sexes are segregated on separate thalli, are also known. Finally, with homothallic fungi that fruit with difficulty in ordinary culture some advance on the problem has been made by students of the nutritional requirements of fungi, particularly under the leadership of Lilly (3). These workers have found that supplementation of of the substrate with vitamins often leads to fruition in cultures that have hitherto been considered sterile or lacking in one or more spore stages
