18 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 



PHYSIOLOGY. 



Only preliminary work was done on the physiological phases of the 

 problem, and since, as a rule, the tests were not made in duplicate, 

 only a brief summary of the results will be presented. 



NUTRITION. 1 



In studying the nutrition of the fungus, use was made of a standard 

 nutrient solution containing molecular -=- 8 ammonium nitrate, mo- 

 lecular -=-20 potassium acid phosphate, molecular -r- 50 magnesium 

 sulphate, molecular -=- 1,000,000 iron chlorid, and about 5 per cent 

 sucrose. By substitutions within this formula, the effect of the 

 omission of an element was determined. The fungus was grown in 

 parallel series with Aspergillus niger in flasks containing about 50 

 c. c. of the medium. Dry-weight yields were used as criteria. 



Using the full nutrient solution, it was found that in 24 days 

 Colletotrichum produced only about one-twentieth as much dry- 

 weight yield as did Aspergillus in 15 days, but after a much longer 

 interval the yield of Colletotrichum was almost as great. No sporu- 

 lation of the latter was secured and it was evident that a liquid 

 medium was not well adapted to the development of Colletotrichum. 



As a result of substitutions in the formula it was found that car- 

 bon, nitrogen, potassium, and phosphorus were essential to the 

 growth of Colletotrichum, while magnesium was needed in only very 

 minute quantities. Sulphur and iron were not needed in excess of 

 the amounts present as possible impurities. Colletotrichum seems 

 to be less sensitive to a lack of magnesium and sulphur than Asper- 

 gillus and more sensitive to a deficiency of potassium and phos- 

 phorus. 



Substituting other carbohydrates for sucrose, so that an equal 

 amount of carbon was present, it was found that Colletotrichum, 

 unlike Aspergillus, uses cornstarch to exceptional advantage. The 

 other carbon sources, listed in descending order of suitability, are 

 inulin, maltose, dextrose and galactose, salicin, glycerol, and lactose. 

 Sucrose should probably be ranked with the dextrose and galactose. 

 For Aspergillus the order would be sucrose, inulin and maltose, dex- 

 trose, cornstarch, galactose, tannin, glycerol, lactose, and salicin. 

 Colletotrichum was unable to utilize tannin. 



Further proof of the preference of Colletotrichum for the more 

 complex carbon compounds was afforded by its abundant develop- 

 ment on xylan as a carbon source. Using xylan prepared from straw 

 in place of sucrose in an amount such that only one-fourth as much 

 carbon was available as in the full nutrient solution, a similar dry- 

 weight yield of fungus mycelium was obtained. Xylan appears to 

 be fully as suitable a carbon source as cornstarch. 



i The testa relative to nutrition and the effect of copper sulphate were made raider the dinri ion of. Prof. 

 J. 15. Overton and Dr. J. I', liennet I , of the. University of Wisconsin. 



