142 BOTANICAL GAZETTE [august 



CONTRAST SERIES F 



In this series culture no. 3, which was shown to be plus in series 

 B, was contrasted as in the previous series with all the remaining 

 numbers and formed zygospores with nos. 9-11, 14, 16, 17, 20, 

 and 21. Culture no. 11, which up to this time had failed to react 

 with plus strains and had been considered neutral, formed normal 

 zygospores when contrasted with- no. 3. The conditions were the 

 same as those of the previous experiments so far as it was possible 

 to duplicate them. This series, as well as the others, was repeated 

 several times, and in no instance did no. 11 form zygospores with 

 9, 14, or 21, the plus strains used in series B, C, and D. 



CONTRAST SERIES G 



Culture no. 10, which was determined to be plus in series B 

 when contrasted on agar plates with the different strains, formed 

 zygospores with nos. 3, 7, 8, 12, 13, 18, 19, 21-23. Cultures 18, 

 19, 22, and 23 had not formed zygospores with any of the other 

 strains of C. bertholletiae previously tested, and therefore were 

 considered as neutral. Since, however, in this series they formed 

 zygospores with no. 10, they must be assumed to be minus. The 

 question here arises, why if they are minus have they not con- 

 jugated with cultures nos. 3, 7, 9, and 14, which were all proved 

 to be plus by the contrasts made in series B ? 



As had previously been stated, the cultures used in these 4 

 series were obtained from transfers made by touching single heads 

 with a sterile needle and transferring directly, but in order to 

 preclude the possibility of a mixture of strains, on January 3, 

 191 7, single- spore cultures were made from cultures 3, 9, and 21, 

 which were selected from the critical numbers used in the contrast 

 series described. These cultures were made by the poured plate 

 method. The germinating spores were located with the compound 

 microscope, and were picked out by means of a line needle and 

 transferred to culture tubes. I obtained 3 single spore cultures 

 of no. 3, 2 cultures of no. 9, and 4 cultures of no. 21. On January 

 27, 191 7, the following contrast cultures were made with these 

 single spore mycelia. 



