202 THE ASCOMYCETES 



Another ^^'ell-kno^^-n genus, which many mycologists place 

 among the Fimetariaceae, is Neurospora. Its conidial stage is 

 monilioid. The pink bakery mold, N. sitophila, has 8 spores, 

 ^\•hereas N. tetrasperma has 4. Kno\\'ledge of sexuality in these 

 species comes from the accounts by Dodge (1927, 1932, 1935), 

 Colson (1934), and Backus (1939). By isolating each of the 

 ascospores from individual asci of N. sitophila and mating their 

 mvcelia in cultures, Dodge (1927) showed that the species is 

 heterothallic. Similarly, each ascospore of N. tetrasperma nor- 

 mally contains two nuclei differing from each other in compati- 

 bility. When this species is grown in monosporic cultures, there- 

 fore, it is found to be hermaphroditic. Occasionally, however, it 

 forms dwarf ascospores, each having only one nucleus, and these 

 are not totipotent. They are of either class A or class B in their 

 sex reaction, and thalli of both classes must be grown together to 

 produce perithecia. 



Both N. sitophila and N. tetrasperma form coiled ascogonia 

 with branched trichogynal hyphae, although Colson (1934) con- 

 cluded that they may not be formed in heterothaUic races of N. 

 tetrasperma. Both also form spermatia. Dodge (1935) appHed 

 spermatia from class A cultures of N. tetrasperma to cultures of 

 class B and secured perithecia in the loci of application, indicating 

 that spermatia function in fertilization. He also found that 

 monilioid conidia can function in fertilization, or that "young 

 aerial hyphae or even trichogynes or trichogynous hyphae, if 

 they come in contact with trichogynous elements of the opposite 

 sex reaction, are capable of effecting fertilization." This tend- 

 ency of "substitute sexuality," as denominated by Backus 

 (1939), was verified in Backus's experiments, in which the archi- 

 carpic stromata became transformed into perithecia after contact 

 with germinated conidia, germinated ascospores, or myceHal mats 

 of the complementary^ sexual strain of N. sitophila. . Moreover, a 

 small group of perithecia was induced to form near the site 

 where a single ungerminated conidium was deposited, just be- 

 yond the advancing margin of the mycelium. The performance 

 of sexual functions is therefore regulated by compatibility factors 

 which prevent self-fertilization. 



It has been suggested that Acanthorhynchiis vaccijiii, causing 

 a rot of cranberries, also belongs in this family. This fungus 

 normally produces perithecia in decaying leaves of its host, and 



