200 BOTANICAL GAZETTE [SEPTEMBER 
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, o.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 to 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. Inno case wasit 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- 
