104 CARNEGIE INSTITUTION OF WASHINGTON. 



approximately the 50 per cent and 75 per cent, respectively, which 

 might be expected on the assumption that the ascidia are produced 

 by a dominant Mendelian determiner. 



Abnormalities in Seeding Beans and in Fruits of Passiflora, hy J. A. Harris. 



These studies are being continued as outlined in previous reports 

 and are being lined up with the selective elimination, fertility, and 

 physico-chemical studies. Material progress in the experimental 

 control of the occurrence of certain of these phenomena by physical 

 and chemical means has been made during the year. 



Mutations in Mucors, hy A. F. Blakeslee. 



Thechief work planned by Dr. Blakeslee was to induce the produc- 

 tion of mutations in mucors by chemical or other forms of stimulation. 

 He was thus led to make extended preliminary studies and to devise 

 new methods. His report on this part of the work is as follows : 



A standard medium was considered necessary that could be ta,ken as 

 representing a favorable or normal substratum, and some 308 different 

 combinations of nutrients (natural and synthetic) were tested. It was 

 discovered that the mucors were unlike the green molds (Penicillium) in 

 that they would not grow well on liquid media nor upon synthetic media 

 in which the necessary elements were supplied in relatively simple chemical 

 substance. An agar nutrient with 2 per cent dry malt extract, 2 per cent 

 dextrose, and 0.1 per cent meat peptone was eventually adopted as a stand- 

 ard medium sufficiently near the optimum value for most forms investi- 

 gated and as nearly constant in chemical composition as any tested upon 

 which the molds would thrive. 



Sexual reproduction in the mucors demands in general the optimum 

 cultural conditions, and the abundance of zygospore formation on a given 

 substratum has been used accordingly as an index of its cultural value. 

 Phycomyces is one of the most demanding forms so far as its requirements 

 for zygospore production is concerned and in consequence is the species 

 which has been most used in the nutrient tests. Peptone, although the 

 usual form in which nitrogen is supplied in culture media, was found to 

 have a slightly inhibitory action on zygospore formation. Meat peptone 

 seemed to be less toxic than either peptone from egg-albumen or Witte's 

 peptone. Nutrients containing peptone which would allow only a poor 

 growth with entire suppression of zygospores could be changed into opti- 

 mum substrata with luxuriant zygospore production by inoculating them 

 with bacteria either before or at the very time of planting the sexual races of 

 the mold. The subject needs further investigation before publication. It 

 is not unlikely, however, that by tryptic action of the bacteria the peptone 

 is further broken down into a condition less toxic and more available to 

 the mold. This seems to be the case in the preparation of media upon 

 which the leprosy organism has recently been successfully cultivated. The 

 action of bacteria may explain why a decoction of horse dung has been 

 found to be one of the best substrata for zygospore production. 



A standard medium having been decided upon, it became necessary to 

 provide against contamination from germs of foreign species in the pedigree 

 cultures. An isolated culture room containing a pure-culture chamber, 



