iqiq] burger— CUNNINGH AMELIA 137 



mentioned. The peculiarity shown by the different strains in 

 their methods of conjugating with each other seems to indicate 

 that the difference in sex in Cunninghamella is quantitative rather 

 than quahtative. If one of the strains is taken as plus and all 

 the others which conjugate with it as minus, there are strains 

 ivhich will conjugate with both plus and minus strains. On the 

 other hand, there are, for example, strains (A) which will not show 

 reaction with certain ones (B) but will in turn react with a third 

 strain (C) which showed a sexual reaction with (B). The abihty 

 of one strain to show an individual selective power in conjugating 

 with certain other strains is interpreted as evidence of a quan- 

 titative difference. Thus, if 2 strains are contrasted whose gametes 

 are compatible a sexual reaction will take place. On the other 

 hand, if 2 strains are contrasted whose gametes are incompatible 

 no sexual reaction will take place. 



Method 



For two years I have been working with Cunninghamella 

 hertholletiae. The cultures were obtained from decaying nuts of 

 Bertholletia excelsa, together with cultures communicated to me 

 by Dr. Thaxter, Dr. Blakeslee, and students in the Harvard 

 Cr^ptogamic Laboratory. Authentic cultures of C. hertholletiae 

 and C. elegans were obtained from Holland. The pure cultures 

 used were obtained by transferring spores with a flamed needle 

 directly from a single isolated head to a slant agar tube. Oatmeal 

 agar was found to give the best results with these forms. The 

 medium was made in the following manner: to every 1000 cc. 

 of water was added 50 gm. of oatmeal. The mixture was steamed 

 for 20 minutes, then strained through a triple thickness of cheese- 

 cloth, and 2 per cent of agar was then added. It was again auto- 

 claved fbr 20 minutes at 15 lbs. pressure, after which it was tubed 

 and sterilized. 



The best results were obtained by placing the contrast series 

 in battery jars, which were lined with moist filter paper and incu- 

 bated at a temperature of 27° C. The contrast series were made 

 by inoculating a Petri dish with 2 strains. It has been shown by 

 Blakeslee that zygospores are formed more readily in moist 



