202 
Journal of Agricultural Research 
Vol. XXI, No 4 
Table VII.— Hydrogen-ion concentrations , expressed in terms of potential hydrogen 
Series 
No. 
Percentage 
of dextrose 
by weight. 
Solution. 
Fusarium 
acumin¬ 
atum. 
Diplodta 
tubertcola. 
Rhizopus 
tritici. 
Mucor 
racentosus. 
I 
f Control . 
A. 12 
4.41 
3 - 89 
3-97 
3. 66 
6- 33 
6. 12 
6- 54 
6. 02 
0 
\ Inoculated. 
4. 24 
3 - 97 
3-89 
3-93 
3 - 7 1 
3 - 96 
3.66 
A . 22 
II 
f Control . 
4.84 
2. 11 
5 - 44 
3-09 
5. 06 
? 21 
10 
1 Inoculated . 
III 
f Control. 
3-89 
2. K 2 
3. 91 
2. 30 
3 - 75 
2. 27 
4 . 07 
3-84 
3 * 72 
4 - 5 ° 
1. 90 
4. 20 
1. 81 
20 
( Inoculated. 
IV 
f Control . 
O' * A 
4 - 30 
3 - 46 
4 - 39 
3 - 13 
4. 28 
30 
( Inoculated . 
V 
| Control . 
4. 10 
40 
( Inoculated . 
' Z . 62 
2. 00 
VI 
f Control . 
3 - 97 
3 * 99 
4. 09 
4. 00 
2. 81 
50 
(Inoculated . 
4. 17 
4. 08 
VII 
60 
f Control . 
4. 12 
\lhoculated . 
Series 
No. 
Percentage 
of dextrose 
by weight. 
Solution. 
Sclerotium 
bataticola. 
Penicilltum 
sp. 
Botrytis 
cinerea. 
Sphaero- 
nema jxm- 
briatum. 
f Control . 
6. 49 
5 - 15 
4 - 54 
A . 21 
6.44 
6.41 
5 - 7 ° 
4 - 37 
5 - 39 
3.81 
5-14 
3 - 9 2 
4 - 79 
3 - 44 
4 - 5 i 
3 * 2 9 
4. 40 
3. 16 
6. 39 
6. 25 
4. 99 
3 - 2 4 
4 - 5 i 
2. 91 
4. 22 
3 - 45 
4. 07 
3 - 9 2 
4. 00 
6. 41 
6. 41 
5 -19 
5 - 50 
5.16 
5 - 05 
A. 10. 
I 
0 
( Inoculated. 
II 
^Control. 
IO 
(Inoculated. 
III 
jControl. 
4-83 
A . 06 
20 
(Inoculated. 
IV 
f Control. 
4. 80 
30 
(Inoculated. 
4. 07 
4. 82 
4 -83 
4 - 52 
f Control. 
V 
40 
(Inoculated. 
3 - 69 
4. 76 
4 - 75 
4-75 
VI 
f Control. 
50 
(Inoculated. 
VII 
60 
f Control. 
(Inoculated. 
No attempt was made to bring the different solutions to a definite or 
uniform hydrogen-ion concentration. What influence the organisms had 
on* the hydrogen-ion concentration was determined by a comparison of 
the controls with the solutions after the removal of the fungous growth. 
That the solutions differed somewhat in their original hydrogen-ion con¬ 
centration is seen from Table VII. Gillespie (jj) in working with differ¬ 
ent strains of the potato scab organism, Actinomyces chromogenus Gasp, 
in culture media of different composition found that the growth was 
slower and less vigorous in a solution with a hydrogen-ion concentration 
of P H 5.2 than in less acid media. It would seem that, although there 
was some variation as regards the tolerance of the different strains to 
acid media, a P H of 5.2 would closely approximate the limit of growth. 
A further interesting fact in this connection also was brought out by 
Gillespie, who showed that cultivated soils of the Caribou loam, which is 
generally free from the scab organism, yield a water extract with P H 
values varying from 4.9 to 5.5 with a mean of 5.2. Meacham (22) found 
