Vol. XXV, No. 6 
274 Journal of Agricultural Research 
the strains from coconut and cacao grew so nearly the same that it was 
impossible to note any marked difference between them. 
On potato dextrose agar a distinct curve of growth for each was pro¬ 
duced, with no growth at a hydrogen-ion concentration of 2 and below, 
and slight growth at 2.4. Above this concentration there was a gradual 
increase in the growth up to 8.8, when a decrease was noted. Between a 
hydrogen-ion concentration of 5.8 and 8.8 there appeared to be no marked 
difference in the extent of growth. Growth still took place at a concen¬ 
tration of 10+. 
The growth between 2.4 and 3.8 was flat, dense, thick, and tough, with 
the production of few chlamydospores and conidia. A fluffy, dense, 
thick growth with few to many chlamydospores and with a smaller num¬ 
ber of conidia was produced between 4.0 and 5.2. The mass of hyphae 
was still fluffy between a hydrogen-ion concentration of 5.6 and 7.8, but 
gradually became thinner, with a surface growth about the edges, above 
these concentrations. At these concentrations many chlamydospores 
and conidia were produced. Between 7.8 and 8.8 the aerial, fluffy 
growth began to disappear. Fewer spores of both kinds were formed. 
Above a hydrogen-ion concentration of 9 the growth was thin, flat, 
being on the surface of the agar, and few to no spores were formed. 
At 10+ it was thin on the surface, and without spores. At all concen¬ 
trations except 10+ the hyphae penetrated and grew in the agar as well 
as upon the surface. 
The optimum for growth appeared to be between a hydrogen-ion 
concentration of 7.4 to 7.8. Good growth was also produced up to 8.8. 
Slight growth took place at an acidity of 2.4. An alkalinity of 10+ did 
not prevent the development of either strain. 
In the Czapeks solution the difference between the initial hydrogen-ion 
concentration and that at the end of the experiment was obtained. 
Control flasks of the solutions without the fungi were also kept. The 
growth at the different concentrations for both the coconut and cacao 
strains was so nearly identical that no real difference could be noted. 
No vegetation was obtained between hydrogen-ion concentrations of 2 
and 3.2. Slight growth started at 3.4 and then gradually increased up 
to 9. Above this the growth gradually decreased, but still was apparent 
in the flasks with an initial concentration of 10 -f. No spores were pro¬ 
duced in the liquid media. The optimum growth appeared to be around 
7.8. 
A marked change in the hydrogen-ion concentration, except in the 
extremely acid solutions, was noted after the fungus had grown in the 
media for 20 days. Between 3.4 and 3.6 the initial and final concentra¬ 
tions were the same. From 4.6, and above, the final concentration 
was less than that of the initial. The solutions with an initial concen¬ 
tration of from 7.8 to 10+ all were brought down to a final concentra¬ 
tion ranging between 7 and 7.9. The controls remained the same except 
for a slight reduction in the concentrations above 7.8. 
These tests show that both strains of the fungus were able to withstand 
a rather large range of concentrations from acid to alkaline. The best 
growth, however, appeared to be somewhat above the neutral point, 
between 7.4 and 8.4. The minimum hydrogen-ion concentration at 
which growth took place was 2.4, and the maximum was 10+ . Plate 
7, B and C, shows the growth at the various hydrogen-ion concentrations. 
