144 BOTANICAL GAZETTE [august 



each other, and therefore are not considered as neutrals. When- 

 ever cultures 25 and 32 were contrasted with culture 34, which 

 is C. elegans, imperfect hybridization took place. It must also 

 be remembered that cultures 25 and 32 are minus, as separated 

 by Blakeslee. It is peculiar that the plus strains of C. echin- 

 ulata and Mucor V. showed no sexual reaction with any of the 

 cultures of C. bertholleiiae. 



Discussion 



During the entire work, although careful search for them was 

 made, no zygospores were obtained in the pure cultures, a fact 

 which indicates that this species is not homothallic. Since the 

 strains show a selective power in conjugating with other strains, 

 however, it is not a heterothallic form as defined by Blakeslee. 



Since it was impossible to get any of the strains of C. berthol- 

 leiiae to react with C. echinulata or Mucor V. as separated by 

 Blakeslee, I had to use the indirect method to determine the 

 sex of the different strains. In contrast series A, no. 25, which 

 is Mucor V. minus, showed a sexual reaction with no. 34, which 

 is an authentic culture of C. elegans. All the cultures which did 

 not react with no. 34 must therefore be considered either of the 

 same sex, which is minus or neutral. 



In contrast series B culture no. 21 formed normal zygospores 

 with cultures 3 and 13, which themselves were proved in contrast 

 series A to be of the same sex as 2 1 . 



On the assumption that the species is dioecious, it is impossible 

 to account for the production of normal zygospores as a result 

 of the interaction of mycelia of the same "sex." The situation 

 is further complicated by the behavior of some of the so-called 

 "neutral strains." 



On the basis of contrast series B, nos. i, 2, 3, 7, 9, 10, 13, 14, 

 16, 17, and 20 are plus. On the other hand, in contrast series A 

 nos. 3, 8, 12, 13, 2*1, 24-26, and 32 were shown to be minus. 

 According to Blakeslee's views, nos. 4-6, 11, 15, 18, 19, 22, 27,, 

 27, 28, 30, 31, and T,T) must be neutral, for they show no sexual 

 reaction with 2 strains which were shown to be plus and minus 

 respectively. 



