Apr., 1922] HOPKINS — HYDROGEN-ION CONCENTRATION 
163 
Experiment 2. Growth on Liquid Media — Phosphate Series 
In order to check the result reported above, a similar experiment was 
performed using phosphate solutions to adjust the reaction. Three periods 
of growth were used in this case instead of one. Four, seven, and fourteen 
days were selected as suitable lengths of time. At the end of each of these 
periods a series of cultures was removed and the pn values and dry weights 
of the mycelium were determined as before. 
The culture solution used contained in one liter: 
KNO3 2.0 g. 
MgS04.7H20 0.5 g. 
Glucose lo.o g. 
In addition, the solution designated as the "acid solution" contained 
9-077 g- KH2PO4 per Hter, and the *' basic solution" contained 11. 616 g. of 
K2HPO4 per hter. This made two culture solutions of ikf/15 concentration 
as regards the acid and basic phosphate respectively. By mixing these two 
solutions in varying proportion the hydrogen-ion concentrations desired 
could be obtained. This was roughly accomplished by using the titration 
curve of Sorensen (14) for phosphate buffer mixtures. For more acid or 
more alkaline mixtures than could be obtained in this way, Mji^ concentra- 
tions of H3PO4 and KOH were prepared in culture solution and added in 
varying proportions to the "acid" or "basic" solution respectively. 
Table 2. Hydrogen-ion Concentration and Growth of Gibberella Saubinetii in Liquid Media 
in which the Reaction was Adjusted with Primary Potassium Phosphate, Secondary 
Potassium Phosphate, Phosphoric Acid, and Potassium Hydroxide 
Results after 4 Days 
Results after 7 Days 
Results after 14 Days 
Ph 
Drv Weight 
Ph 
Dry Weight 
Ph 
Dry Weight 
^Mg.) 
(Mg.) 
(Mg.) 
2.8 
0.0 
2.77 
0.3 
2.8 
2.2 
2.9 
0.6 
2.9 
0.8 
3.15 
3-6 
3.05 
0.0 
3-1 
1.8 
3-25 
17.2 
34 
1.8 
3-47 
3.8 
3-85 
70.6 
4-25 
6.0 
4.6 
47.4 
5-0 
42.2 
4-75 
4.8 
4.6 
23-4 
5-4 
70.4 
5-35 
5-4 
5-07 
20.2 
5.6 
72.2 
5-7 
7.0 
5-45 
15.2 
5.75 
67.8 
6.25 
9.2 
6.25 
14.4 
5-75 
75-0 
6.95 
3-0 
6.85 
28.2 
7.15 
71. 1 
7.1 
7.0 
7-1 
48.8 
7-45 
66.1* 
7.1 
10.6 
7.15 
317' 
7.55 
73-2 
7.1 
2.8 
7.2 
13-6 
7-7 
47.8 
7.15 
7.8 
7.2 
3-2 
7.75 
70.8 
7-15 
0.8 
7.4 
2.2 
7.2 
12.4 
7-4 
2.2 
7.2 
3-0 
* Average of three determinations. 
