864 
Journal of Agricultural Research 
Vol. XXIV, No. 10 
growth and fruiting on Irish-potato decoction were good but somewhat 
inferior to what they were on bean, carrot or turnip. The growth was 
poorer on sweet-potato decoction than on any of the vegetable prepara¬ 
tions, The growth on the three synthetic media and on beef bouillon 
was not as good as on the vegetable decoctions. A better growth was 
made on beef bouillon than on Czapek’s, Pfeifer’s, or Richard’s solutions. 
The poor growth on Czapek’s solution was rather surprising in view of 
the fact that Rhizopus usually grows well and fruits abundantly on it. 
The time for terminating the experiment was gaged by the stage of 
fruiting of the fungus. It was shown by Brown {2) and by Harter and 
Weimer (9) that the maximum amount of the macerating principle was 
contained in the mycelium just at or just preceding fruiting. Fruiting 
began a little earlier on the vegetable media than on the synthetic ones, 
consequently the experiments in which the vegetable media were used 
were terminated usually one day sooner than the others. 
hydrogbn-ion concentration 
The hydrogen-ion concentrations of the uninoculated solutions and 
the solutions on which the fungus grew are shown by Table I. 
Table I.— Hydrogen-ion concentration of inoculated solutions and controls {uninoculated 
at the end of the experiments in terms of Ph) 
Media. 
Experiment i. 
Experiment 2. 
Control. 
Inoculated. 
Control. 
Inoculated, 
String-bean decoction. 
4. 88 
7. 82 
4. 80 
7 - 99 
Prune decoction. 
3 - 95 
3. 58 
3*91 
3 - 53 
Irish-potato decoction. 
5. 68 
7. 48 
5. 60 
7, 80 
Carrot decoction. 
5. 18 
4 - 36 
4. 98 
4 - 47 
Turnip decoction.:. 
5 - 05 
4-03 
4- 83 
4. 26 
Sweet-potato decoction. 
5. 22 
3 - 24 
5 - 05 
3-31 
Czapek's solution. 
4. 84 
2.34 
4. 14 
2. 47 
Pfeffer’s solution. 
3 - 53 
2. 56 
3- 48 
2. 61 
Richard’s solution. 
3-44 
2. 
3 - 36 
2. 46 
Beef bouillon. 
8. 29 
8. 18 
8, 04 
8. 52 
A survey of Table I shows that there is about as close an agreement 
in Ph values between the two experiments as could be expected from 
two experiments carried out at different times and under somewhat 
different conditions. The greatest variation noted is in the controls in 
connection with Czapek’s nutrient solution. The solutions for the two 
experiments were prepared at one time so that those used for the second 
experiment stood for some time longer. A certain amount of evapora¬ 
tion would probably take place and chemical reactions are not unlikely. 
A further examination of the table reveals other curious facts with 
respect to the hydrogen-ion concentration. The growth of the fungus 
caused some change in the hydrogen-ion concentration of all the solu¬ 
tions although in the case of beef bouillon and prune decoction it was not 
large. On the other hand, the change produced by the fungus when 
growing on string bean and Irish potato decoction and on Czapek’s solu¬ 
tion was quite marked. In experiment i in string-bean decoction the 
hydrogen-ion concentration was decreased from Ph 4.88 to 7.82 and 
