i6o 
Journal of Agricultural Research 
Vol. XXV, No. 3 
The change in the amount of dextrose was not large in any case, being 
approximately the same in the cultures held in the light and in the dark. 
The weight of the mycelium was not characteristically different, although 
a little more on an average was actually produced in the dark than in 
the light. One outstanding feature of these results to which attention 
should be directed is the short time required for the fungus to reach its 
maximum growth. If the dry weight of the mycelium produced in 3 
days is compared with that produced at the end of succeeding days, it 
will be seen that the fungus has practically completed its growth in 4 
days. The hydrogen-ion concentration of the substrate increases very 
little after the fourth day. There is also very little decrease in the sugar 
consumed after that time, which shows that the organism grows very 
rapidly at first. 
The above results show that R. tritici greatly increases the hydrogen- 
ion concentration when grown on Czapek’s nutrient solution and that 
the acidity reaches its maximum in from 3 to 4 days. Additional inves¬ 
tigations which will not be given in detail have shown that the solution 
still remains acid at the end of 10 days and does not tend to become 
alkaline, as is the case with solutions on which some other organisms 
have grown. Since R . nigricans is a species of great economic im¬ 
portance, similar experiments were carried out with it, the results of 
which are shown in Table IV. 
Table IV .—Showing the P H value of the solution of sweet-potato decoction on which 
R. nigricans had grown for different lengths of time 
Period of growth (hours). 
• 
O 
7 
24 
3i 
48 
55 
76 
96 
240 
R. nigricans.\ 
Tfinnilntinn solution. 
5- 48 
5-48 
5.05 
5 os 
5.48 
5-48 
5- 08 
5- 07 
5.48 
4.44 
5.02 
5- 48 
3-88 
5- 20 
5*45 
3- 62 
5. 22 
5* 93 
5- 45 
3. 70 
s- 07 
6.46 
6. is 
5 '43 
Control . 
R. tritici: 
TtiruMilafinn colution . 
3- 59 
Pnntrnl . 
The solution upon which Rhizopus nigricans had grown showed slight 
increases in acidity at the end of 24 and 31 hours, after which the hydro¬ 
gen-ion concentration began to decrease, reaching a final concentra¬ 
tion in 4 days, considerably less than that of the original solution. 
INFLUENCE OF BOTRYTIS CINEREA ON HYDROGEN-ION 
CONCENTRATION 
Botrytis cinerea Pers. has been used in experiments in which it was 
found to produce a substance capable of dissolving the middle lamellae 
so that coherence of the cells was completely lost. Smith (74), Brown 
(2), de Barry (1), Nordhausen (rj), Kissling (5), and others have made 
a study of the parasitism of this fungus and its mode of action. The 
results obtained by these different investigators are not entirely in har¬ 
mony. Smith, for example, claimed that in old mycelium of Botrytis 
cinerea as much as 2 per cent oxalic acid was produced, which he sus¬ 
pected to be responsible for some of the conditions noted. He appears 
to have discovered a twofold action on lettuce tissue, one which results 
