JOHN R. RAPER 3^3 



heitnalis and Phycomyces Blakesleeamis was investigated by Schopfer (65) 

 and Ronsdorf (60) respectively. In P. B/af{esIeeafms phloroglucin com- 

 pletely suppressed sexual activity while histamine greatly augmented 

 the production of zygospores. The only demonstrated instance of a 

 significant effect upon the sexual process of a fungus by a mammalian 

 sex hormone is that described by Plumb and Durrel (43) in which 

 oestrin or theelin was shown to suppress completely the production of 

 gametangia and zygospores in Rhizopus nigricans. 



The abundance of perithecia of Melanospora destruens was shown by 

 Hawker (8,21,22) to be greatly increased by the presence of contaminat- 

 ing colonies of Botrytis, Fusarium, Gleosporiiim, Sclerotinia, and Peni- 

 cillium. Lentil extract also stimulated perithecial formation; this effect 

 was proved to be due to thiamin and biotin, each of which alone would 

 support vegetative growth in a synthetic medium while both were 

 required for sexual activity. Inositol, which was shown to have no effect 

 on M. destruens, was shown by Raper (45,47) to increase the intensity 

 of the sexual reaction in matings of Achlya ambisexualis in an agar 

 medium. 



The requirements for sexual reproduction in Phycomyces Bla\esleeanus 

 was the subject of an extensive investigation chiefly by Schopfer and 

 Robbins and their associates during the decade 1932-42. Thiamin or 

 its pyrimidine component is required for vegetative growth but other 

 accessory substances were considered necessary for zygospore formation 

 (66,67,68). Such factors were obtainable from numerous natural sub- 

 strates including malt, oats, potatoes, and agar (52,53,54). The activity 

 in potatoes consisted of two mutually augmentative factors, Zi and Z2, 

 the former adsorbed on Norite, the latter not adsorbed on Norite (56). 

 Factor 7i was identified as hypoxanthine (58) and was replaceable by 

 guanine (57), a closely related purine-base compound. The contention 

 that specific accessory substances were required for zygospore formation 

 was disputed by Leonian and Lilly (34) who claimed that sexual sterility 

 resulted from nutritional inadequacies. Zygospores were formed in a 

 synthetic medium containing thiamin, sugar, and only one of a number 

 of amino acids (aspartic acid being the best one). Succinic acid increased 

 the abundance of zygospores while ammonium nitrate completely sup- 

 pressed their formation; the two effects were partially antagonistic. 



The most completely elucidated interspecific stimulation of sexual 

 processes is that of Zygosaccharomyces sp. described by Nickerson and 



