Jan. 17, 1916 
Plenodomus fuscomaculans 
735 
given growth but no fruiting bodies. Once this relation of the organism 
to acid and alkali was known, previous experiments could be reviewed 
in the light of it and the behavior of certain chemicals explained. 
Ten c. c, of a 5 per cent gum-arabic solution was autoclaved in a 
series of preparation dishes. The solution received sterile chemicals to 
give concentration as shown in the table and was inoculated with a 
spore suspension. 
Table? XV .—Effect of acidity and alkalinity: Test with various chemicals 
[Time, 1 month] 
Chemicals. 
Concentration. 
Reaction. 
Number of 
pycnidia. 
Growth. 
Gum-arabic solution plus— 
Potassium acid phosphate. 
Ml200 . 
+ 
+ + 
++ 
Potassium acid phosphate. 
Ml 200 each 
+ 
+ + + 
+++ 
+ Sodium acid phosphate. 
Sodium acid phosphate. 
Ml 200 . 
+ 
+ + 
+++ 
Dibasic potassium phosphate. 
Ml200 .. 
— 
0 
+++ 
Check. 
Sodium hydroxid. 
“5 
+ 
0 
++ 
+ 
This experiment, if it be permitted to draw conclusions by compari¬ 
son of salts with a similar anion or cation, indicated that the specific 
effects in pycnidium formation were not due to any specific ion, for if 
potassium were the influential ion, then we should get no effects with 
the similar sodium salt. More conclusive still was the effect of the 
dipotassium phosphate as contrasted with the dihydrogen salt. Here 
the same ions were concerned, but in different proportions. The ex¬ 
periment shows the extreme sensitiveness of this organism to alkalinity, 
since a reaction of — 5 was sufficient to cause absence of pycnidia. 
A study of the reaction of some of the common media, as given in 
Table XXV, shows how reaction controls not only reproduction, but 
growth as well. Of the complex media tried the most favorable for 
pycnidium production was a couple of corn grains autoclaved in 10 c. c. 
of water. Aside from the nutrition relation, which will be discussed later, 
the acid reaction is largely responsible for the excellence of this medium; 
but the time when this reaction is most effective is at the period when 
growth has covered the medium, not the mere reaction at the start. 
Corn broth shows at the start an acidity of + 8, and after a month the 
reaction is still acid, +5. As is seen from Table XIV, this is a favor¬ 
able condition for pycnidium production. Pea solution at the begin¬ 
ning of a period of culture showed an acid reaction of +8, while oats 
showed at the start a reaction of +5. The latter showed after a month 
a reaction approximately neutral. It will be seen from Table XXV 
that oats were a correspondingly poorer medium than corn. Pea broth, 
on the other hand, showed a reversal of condition, and after a month 
