762 Journal of Agricultural Research voi.xx.No. 10 



studies. For some parts of the work Czapek's nutrient solution 

 was preferable, since it was then possible to cultivate the fungus in a 

 substrate of known composition. On the other hand, the fungus made 

 a luxuriant growth on sweet potato bouillon, and for experiments, such 

 as the influence of temperature on secretion, this medium was usually 

 employed. 



The fungus was grown in 2-liter Brlenmeyer flasks containing about 

 750 cc. of the sterile solution, on which enough fungous felt was pro- 

 duced to carry out several comparative experiments. 



Preliminary experiments showed that the fungus grew poorly on a 

 solution with sodium nitrate and cane sugar as a source of nitrogen and 

 carbon, respectively. Ammonium nitrate was therefore substituted for 

 sodium nitrate and glucose or potato starch, or both, for cane sugar in 

 Czapek's nutrient solution. The composition of the solution as finally 

 prepared is as follows: 



Water j, 000. 00 cc. 



Magnesium sulphate (crystals) . 5ogm. 



Potassium acid phosphate 1. 00 gm. 



Potassium chlorid . 50 gm. 



Ferrous sulphate .01 gm. 



Ammonium nitrate 5. 00 gm . 



Glucose, starch paste, or both, in varying amounts to suit the require- 

 ments of the experiments as a source of carbon. 



The sweet potato bouillon is prepared as follows: To the peeled 

 potatoes add double the weight of water; steam for one hour, then 

 squeeze out the liquid through gauze; steam a second time, filter into 

 flasks, and autoclave for 20 minutes at 13 pounds pressure. The sweet 

 potato bouillon always contains a considerable quantity of reducing 

 sugar and starch paste. 



Rhizopus tritici grew well on both of these solutions and produced a 

 thick, heavy felt in from 7 to 10 days at a temperature of 25 to 35°C. 

 The better growth was made on the sweet potato bouillon. Contrary 

 to what might be expected, starch paste was more efficient as a source 

 of carbon in Czapek's modified nutrient solution than glucose. The 

 organism was grown in incubators, the temperatures of which did not 

 fluctuate more than 1 °. 



At the end of the growth period the mycelium, which formed a thick 

 felt on the surface of the medium, was removed and washed in running 

 water for about 15 minutes. It was treated subsequently according to 

 Dox's (9) * modification of Albert and Buchner's " acetondauerhef e " 

 method. After washing, the mycelium was stirred constantly in an 

 excess of acetone for 10 minutes, squeezed as dry as possible, and treated 

 a second time for 2 minutes in a fresh supply. This acetone was removed 

 as in the former case, and the mycelium was treated with ether for 3 



1 Reference is made by number (italic) to " Literature cited," p. 784-786. 



