$6 Research Bulletin No. g 



being equal, would render it a much more formidable enemy of the 

 potato plant than an organism without this ability, or possessing it 

 to a less degree. This problem was attacked by making a study 

 of the carbon sources of the organisms. The data reported here 

 are only a beginning of this phase of the problem. 



Fifty cc. of nutrient solution were measured quantitatively into 

 200 cc. Erlenmeyer flasks with a pipette. The flasks were then 

 plugged with cotton, covered with tinfoil, and autoclaved. After 

 cooling, 0.5 gm. of carbohydrate material was transferred quanti- 

 tatively into each flask, and the flasks covered again with tinfoil 

 and sterilized in a Freas oven by heating at 85 C. for one hour 

 every 12 hours, for 6 consecutive days. The solutions were then 

 incubated at 25 C. for 48 hours, so as to allow any contamina- 

 tions present to appear. Low sterilization temperature was used to 

 reduce hydrolysis of carbohydrates to a minimum. 



The dry weight determinations were made by the methods out- 

 lined above. It was found advisable to kill two cultures of each 

 set after 6 days, for the striking differences in rate of growth between 

 the two organisms that were observed during the first 48-120 hours 

 were obliterated by prolonged growth. The other 3 cultures were 

 killed after 12 days' growth. The dry weight values do not show 

 the differences in habit and rate of growth in the cultures as strik- 

 ingly as they appeared to the eye. In many cases a visible growth 

 was not determinable as dry weight. This is readily appreciated 

 when we consider that moisture determinations indicated that the 

 dry weight varied between 10 and 20 per cent of the wet weight. 



In the controls, consisting of the plain mineral medium without 

 carbon material, F. oxysporum made a weighable growth in 12 days, 

 though not in 6 days, while F. trichothecioides made no weighable 

 growth even after 12 days. Another important observation was 

 made. In no case was it necessary to reinoculate with F. oxysporum, 

 while many F. trichothecioides inoculations failed. The latter 

 undoubtedly is the slower starter and much more poorly equipped 

 for sure and quick infection than the former. 



The figures in tables V-VIII represent milligrams of dry weight 

 of material formed, except in those cases in which per cent is written. 

 In such cases (cork, cellulose, and hemicellulose) the figures repre- 



