INov. 1, 1925 
Ophiobolus graminis and Take-All of Wheat 
809 
ion concentration. In the solid medium, only initial determinations 
were made, but in the liquid media both initial and final Ph values 
were determined. As soon as possible after adjusting the medial 
they were inoculated with a uniform quality and amount of inoculum, 
namely, young, vigorous mycelium on blocks of agar 1 mm. square. 
Potato-dextrose agar with hydrogen-ion concentrations in rather 
regular steps from P H 3.0 to P H 10.0 +was used. The media were 
made as usual, except only one-half the required quantity of water 
was added at first. Equal quantities of the concentrated agar were 
placed in the flasks, each of which was plugged, properly labeled, 
and sterilized in the autoclave for 40 minutes at 8 pounds pressure. 
The quantities of acid or alkali necessary to bring the medium in 
each flask to the desired reaction was calculated and the addition 
subsequently made. Calculated amounts of water were then added 
to the flasks to bring the medium in each to the proper dilution. 
This method allowed adjustment of media to various hydrogen-ion 
concentrations by the addition of either acid or alkali without 
materially affecting concentrations and ratios of the nutrients. 
Equal quantities of the agar were then poured into Petri dishes, 
which were properly labelled. Sufficient agar remained in each of 
the stock flasks for hydrogen-ion determinations, which were made 
immediately at room temperature. Each agar-poured plate was 
inoculated as just described and then incubated under glass bell 
jars in diffused light at room temperature. At the end of seven days, 
at which time the largest colonies nearly covered the agar surfaces, 
the diameter of the colonies was measured. The resulting data are 
given in Table II, and the averages from Series 3, a-f, are shown 
graphically in Figure 4. 
