322 



GEXET1CS OF FUNGI 



(1927) and Dodge (1927, 1928) isolated each of the eight asco- 

 spores of N. crassa and found that four are (-)-) and the other 

 four ( — ). This discovery left unanswered the question of when 

 segregation of sex factors occurs. Manifestly it might be possible 



Sterile 



Perithecia 



Sterile 



Perithecia 



_-- r- Sterile 



Perithecia 



^.*? Sterile 



Perithecia 



Fig. 52. Schematic representation of a fivc-spored ascus of Pleurage anserina. 

 The small spores are of opposite sex, the large spores of both sexes. If 

 planted on agar plates, the mycelium of each bears both ascogonia and 

 spermatia. The conditions of fertility and sterility are indicated by the 



matings in each culture. (After Ames.) 



to determine this question if each of the ascospores was isolated 

 and it were known what position within the ascus each occupies. 

 Colonies from each could then be mated reciprocally with each 

 of the others. Accordingly Wilcox (1928) employed N. sito- 

 phila in such experiments, finding that (-f-) and ( — ) ascospores 

 alternate in pairs in the series of eight. This discovery indicates 

 that the sex factors are segregated at the second division of the 

 fused nucleus of the primary ascus. 



