212 
Journal of Agricultural Research 
Vol. XXI, No. 4 
and parallel experiments were run in most cases. The culture flasks 
were placed in an incubator held at a constant temperature, and C0 2 - 
free air was pulled through by means of a Richard air pump. The air was 
passed through three bottles containing pumice stone and concentrated 
potassium hydroxid (KOH) and one bottle containing concentrated 
barium hydroxid (Ba(OH) 2 ), the latter being used principally as an indi¬ 
cator to insure that the air was entirely freed of C 0 2 . The air was finally 
washed by being pulled through C 0 2 -free distilled water, from which it 
was drawn into the culture flasks. The culture flasks and trap bottles 
for freeing the air of C0 2 and for washing it were placed in an incubator 
maintained at a temperature of 29 0 C. From the culture flasks the air 
was drawn out of the incubator through glass tubing. It was then freed 
of C 0 2 by being drawn through a series of cylinders containing a saturated 
solution of Ba(OH) 2 . Fresh air, though not in sufficient amount to in¬ 
terfere with the temperature control, was admitted to the incubator 
through a small hole about 1 cm. in diameter. 
The cultures were grown in 1-liter Jena Erlenmeyer flasks stoppered 
with 2-holed rubber corks, through each of which were passed two glass 
tubes which served for the exchange of air. The tubes which admitted 
the air into the flasks extended to within about 1 inch of the surface of 
the medium, while the exit tubes barely projected through the corks. 
CULTURE medium 
A modification of Czapek’s nutrient solution, in which ammonium ni¬ 
trate (NH 4 N 0 3 ) was substituted for sodium nitrate (NaN 0 3 ), was used as 
a substratum. Baker’s C. P. dextrose in approximately 10 per cent 
strength was supplied as a source of carbon. The culture medium was 
prepared according to a method fully discussed in an article by Weimer 
and Harter (23), to which the reader is referred for complete details. 
PREPARATION OP AN EXPERIMENT 
Three 1 -liter flasks, one to serve as a control, were prepared to contain 
300 cc. of the culture medium. After* being plugged with cotton they 
were sterilized by steaming for 20 minutes on three consecutive days. 
Just before inoculation the cotton plug was replaced by the rubber stop¬ 
per with glass tubes attached, and the whole was resteamed for 20 min¬ 
utes. To allow for the expansion on heating and to prevent contamina¬ 
tion on cooling a glass tube of 3-mm. bore, about 8 cm. long, with a small 
bulb about 1 cm. in diameter midway between the two ends, was con¬ 
nected with each of the tubes passing through the cork by means of 
rubber tubing. The bulb was packed with cotton, which while permit¬ 
ting the passage of air served to filter out all contaminating material. 
The cotton was left in the bulb throughout the experiment. 
Inoculations were made with a loop of a heavy spore suspension in 
distilled water or with a bit of mycelium from a young and vigorous cul- 
