April 23, 1920] 



SCIENCE 



405 



* All poasibl« eombinatioiia made. 



various reasons, lias been misinterpreted by 

 the investigator. 



Burger, in a recent paper (11) concludes 

 that sexual dimorphism does not exist in the 

 mucor genus Cunninghamella. He reports 

 finding certain races, among 25 or 26 of 0. 

 iertholetticB studied, which will form zygo- 

 spores with both plus and minus races. In 

 other words a race A will conjugate with 

 race B, B conjugates with C and C conjugates 

 with A, and the family triangle is completa 

 In personal conversation. Dr. Burger has told 

 me that he has found a similar condition in 

 Syncephalastrum. It is not appropriate at 

 the present time to enter into a discussion of 

 Burger's paper. It will be sufficient to say 

 that we have used some of the same strains 

 that he worked with and, except for infections 

 in an early series of contrasts before we dis- 



covered the great danger in Cunninghamella 

 of contamination of a culture with spores of 

 the opposite sex, we have never had results at 

 all comparable with his. The negative results 

 obtained by us do not, of course, prove that 

 sex intergrades or hermaphrodites never occur 

 in diecious species. He would be a rash phi- 

 losopher who would deny to any protoplasm 

 the possibility of reacting in an unexpected 

 manner. They do indicate, we believe, that 

 the occurrence of such sexual conditions must 

 be, at best, a rare phenomenon. In view of 

 the work tabulated in the accompanying table, 

 it seems wisest therefore, to leave out of dis- 

 cussion, for the present, unconfirmed con- 

 flicting conclusions which are based on rela- 

 tively meager material. 



In the first 5 species of the table (those 

 marked with a star) all the possible combina- 



