(Vou. 8 
38 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
interval of 4 weeks are shown in table xxv1, from which it 
appears that on this medium there is a narrow range of reaction 
for favorable growth. Sclerotial formation occurred only at 
Py4.4. 
Sclerotia formation in B1 occurred at Py 3.8, also Py 4.3, 
and much less in the natural solution; but no sclerotia were 
formed at Py 6.7. From Py 2.8 or 3.8 growth declined more or 
less consistently in all strains, as the H-ion concentration was 
diminished. The most notable result among these observations, 
however, is the extensive growth of B1, after 5 days, apparently 
due to the higher temperature. The incubator chamber was 
then lowered to about 24? C., and the third observation was 
made after an interval of 12 days. Some new growth of B1 was 
then apparent at P, 2.8, in which hydrogen-ion concentration 
the remaining strains had failed to make growth. At this time 
TABLE XXVI 
THE EFFECT OF H- peo CONCENTRATION ON THE one OF P1 IN A 
YNTHETIC NUTRIENT MEDIU 
Reaction Pu 2.0 Pa 3.0 Pa 4.4 Pa 6.8 Pu 8.2 
Dry wt. (gms.) No No 0.055 0.025 0.010 
sclerotia formation of B1 was abundant at Pa 4.3, and less at 
Pa 3.8, and the same was true of P1 and H, although the rate of 
growth was much lower. The result after an incubation inter- 
val of 4 weeks is shown in the table, and further discussion is 
unnecessary. 
The effect of H-ion concentration on the growth of the strains 
is rather variable, or rather somewhat related to the media on 
which the fungi grow. It is almost impossible therefore to name 
a definite optimum; nevertheless, the following tentative con- 
clusions may be drawn: No marked specialization as to favor- 
able H-ion concentration was observed, although B1 had wider 
range on the acid side; and (2) in general, these fungi grew well 
on acidulated media, as observed by Duggar (799), the favorable 
hydrogen-ion concentration being about P, 3.8. 
