204 
Journal of Agricultural Research 
Vol. XXI, No. 4 
cent of glucose and starch, respectively, as a source of carbon and with 
sweet potato bouillon. The fungus was allowed to grow io days, when 
the felt was removed and the dry weight determined. The Czapek’s 
nutrient solution had a hydrogen-ion concentration of P n 3-°7 previous 
to inoculation. After a io days’ growth the acidity had increased to P n 
2.05. The solution was sterilized by autoclaving and was then reinocu¬ 
lated with the same organism, but no growth resulted. Repeated 
inoculations were made, but no growth resulted. No appreciable increase 
or decrease in the Pn value of the solution resulted from the autoclaving 
either in Czapek’s solution or in the sweet potato bouillon. Although 
the fungus would not grow, there remained a considerable quantity of 
glucose and starch in the solution. In a 2-liter flask containing 1,000 cc. 
of solution 1.28 gm. of dried mycelium were produced. 
The sweet potato bouillon had an original P H value of 5.17, which was 
increased by a 10 days’ growth to 3.12. The dry weight produced on 
1,000 cc. of solution in a 2-liter flask amounted to 3.59 gm. The solution 
was sterilized by autoclaving and was reinoculated. At the end of 10 
more days the P H value was 3.08 and the dry weight was 1.33 gm. This 
operation was twice more repeated, and the Ph values after two more 
periods of 10 days’ growth were 3.11 and 3.05, respectively. The dry 
weight of the mycelium in the former case was 0.2536 gm., and not 
enough was produced in the latter to determine. Glucose and starch 
still remained in the solution. It is seen that the hydrogen-ion concen¬ 
tration did not increase materially after the first 10 days’ growth, while the 
actual amount of dry weight of material greatly decreased. 
OSMOTIC CONCENTRATIONS OF THE SOLUTIONS 
Table VIII shows the osmotic pressures in atmospheres of the sugar 
solutions at the end of the experiments. These values were determined 
for the first five series of each organism. There was so little growth in the 
highest concentrations that they were not considered of sufficient im¬ 
portance to justify the determination of their osmotic pressures. 
Attention was previously called to the fact that fungi can germinate and 
grow in a sugar or salt solution far more concentrated than that of the cell 
sap of its host. The literature is replete with instances of certain fungi, 
such as species of Penicillium and Aspergillus, which are able to grow on 
concentrated sugar solutions. All the organisms discussed in this paper 
will germinate on a solution of glucose with an osmotic concentration 
several times greater than that of the cell sap of the sweet potato. 
An examination of Table VIII shows that these fungi grew in solutions 
with a maximum osmotic pressure varying from 81.33 to 101.46 atmos¬ 
pheres. It will be noticed also that in general Fusarium acuminatum and 
Mucor racemosus increased, while all the other organisms decreased the 
osmotic concentration of the solutions during a period of two weeks’ 
growth. Some exceptions in this connection should be noted. F. 
