The wild-type strains of Neurospora crassa first isolated by Dodge, Abbott & Chilton were found to differ in the range of temperatures over which protoperithecia were produced; similar results were obtained with two recently isolated wild strains of a species of Neurospora. The ability to develop protoperithecia at 30° was found to be controlled by at least two genes in reciprocal crosses between two wild types differing in this character. A correlation of these observations with the reported features of tyrosinase production is discussed. Certain mutant strains backcrossed repeatedly to a wild-type strain gave exceptional results at 30°. Preliminary observations suggest that the part played by nicotinamide in the sexual cycle may be connected with some of these exceptions. Temperature did not obviously affect ascus development in outbred crosses between Lindegren and Abbott wild-type strains. With inbred crosses ascus development was controlled by several factors which were temperature sensitive and differed in degree of effect in reciprocal crosses. In most strains tested 20° was the optimum temperature for normal ascus development. At higher temperatures gross abnormalities were observed including asci with more than eight spores.
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