1922] Notes on Sclerotium Rolfsii Sacc. 169 



while those of the center of the sclerotium retain their hyphal char- 

 acter and are separated by large air spaces (fig. -1). The mature 

 sclerotia are dark brown in color, globose to elliptical, and I/2 to 

 11/2 millimeters in diameter. 



Taubenhaus* suggests the existence of plus and minus strains of 

 the fungus and the necessity of a "sexual act" in the formation of 

 the ^:clerotia. If proved, this would indeed be an interesting con- 

 dition, entirely new among fungi, and well worthy of serious study. 



The absence of any spore form made the task of separating pure 

 strains for the study unusually difficulty If an ordinary branched 

 filament were used, one could hardly be positive that parts of other 

 filaments were not included as anastomosed branches. 



In pursuance of the plan finally hit upon several sclerotia from 

 an old culture, obtained originally from a wilted pepper plant, were 

 planted on agar plates which were then inverted and placed in a cul- 

 ture room until considerable aerial growth had formed under the 

 sclerotium. A few filaments from this growth were picked up on the 

 point of a flamed needle which was then dragged across a sterile agar 

 plate. The plate was then inverted on the stage of the microscope ; 

 and, with the low power objective, single unbranched threads were 

 located and their position indicated bj' ink marks on the bottom of 

 the plate. Blocks of the agar, each containing a single thread, were 

 then cut out with a flamed scalpel and transferred to another plate 

 of sterile agar. 



In this way fifty short filaments were isolated and planted. The 

 plates were placed in an incubator and examined under the micro- 

 scope at least once every twenty-four hours for evidence of growth 

 or of contamination. Most of the number either died or showed con- 

 tamination within a few days, but five lived and produced new 

 growth. In these five cases the torn ends of the threads died and the 

 new growth developed from two or three cells remaining alive in the 

 center. 



After growth was well started all five were transferred to tubes 

 of steamed bean pods where, after a few days, each had produced 

 sclerotia in great abundance. Transfers were then planted on plates 

 of peptone beef extract agar — three colonies to each plate, two of A 

 and one of B, etc., throughout the series; so that colonies of each strain 



Taubenhaus, .7. J. 1. c. v. 136. 



