[Vor. 7 
300 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
a reduction has been found by Duggar (unpublished data) to 
have no appreciable effect upon the growth of fungi. 
The nutrient solutions were all prepared by adding 600 cc., 
instead of 1000 cc., of distilled water. This method allowed 
dilutions of the various solutions by additions of regulated 
amounts of acid or alkali and water for the adjustment of vari- 
ous H-ion concentrations without affecting materially the con- 
centrations of the nutrient salts or constituents. 
It is possible to obtain a wide range in the H-ion concentra- 
tions of the solutions by adding an alkali and a mineral acid 
in successively increasing quantities. The addition of the mono-, 
the di-, or the tri-basic potassium phosphate as suggested by 
Zeller, Schmitz, and Duggar ('19) was found to give results 
within a certain range, but additions in too large amounts were 
necessary to produce extreme concentrations. Therefore, since 
such a decided variation in the composition of the nutrient 
solutions undoubtedly would have existed, it seemed undesir- 
able to adopt this method in the experiments under investi- 
gation. 
From preliminary experimentation relative to the adjust- 
ment of H-ion concentration in media of alkaline reactions, 
the most satisfactory results were obtained by using N /5 KOH, 
and an alkali of this strength has been employed in all of the 
experiments except in the case of Czapek's solution. Here, 
the buffer action was less than that in the other nutrient solu- 
tions, consequently N/20 concentration was more conveniently 
and accurately applicable. In all the experiments, however, 
N /5 HCl was favorable for varying the reactions on the acid 
side. In the case of Czapek's solution, the reactions were also 
varied by means of N/1 H:PO, and N/20 NaOH. These re- 
sults so nearly paralleled those obtained with the above acid 
and alkali that it was deemed unnecessary to continue this 
aspect of the experiment with the other nutrient solutions. 
Inasmuch as it is generally admitted that sugars readily 
react with acid or alkali when heated under pressure, the nutri- 
ent solutions and the acid and the alkali were sterilized sep- 
arately. Thirty eec. of the nutrient solution together with the 
desired amount of water, as indicated in the tables, were put 
into small flasks, plugged, and sterilized. After cooling, the 
