Peb. 16, 1924 
Flag Smut of Wheat 
467 
RELATION TO HYDROGEN-ION CONCENTRATION 
Many investigators have studied the effect of the acidity of the medium 
on the germination of fungous spores, but little is known concerning the 
behavior of the smut fungi in this connection. 
Webb (54, p . 326) has stated that the spores of Ustilago avenae (Pers.) 
Jens, did not germinate readily in potassium phosphate solutions of 
different hydrogen-ion concentrations. In mannite solutions, however, 
the spores germinated within the range P H 2.4 to 8.2 with an optimum 
at P H 6.2. Sporidia were formed most abundantly from P H 5.4 to 7.0. 
The writer has observed that the spores of Urocystis tritici did not 
germinate readily in potassium phosphate solutions, but they did so in 
certain of them after the addition of small quantities of a stimulatory 
agent. 
Spores were sown in approximately 1 % per cent potassium solutions. 
Varying amounts of 
M 
5 
M 
potassium hydrate and — phosphoric acid were 
5 
used in making a series in which the hydrogen-ion concentration varied 
from P H 2.4 to 9.6. Final selection of the solutions was made after 
potentiometer determinations of the hydrogen-ion concentrations. 
Two series of observations were made. In the first the spores were 
sown directly in the solutions and five days later a film of benzaldehyde 
was added to each dish in the manner already described. In the second 
series the spores were presoaked in distilled water for five days before 
they were transferred to the phosphate solutions. Benzaldehyde was 
then added as in the first instance. The spores were nine months old at 
the time of testing, and the cultures were kept at from 20° to 22 c C. 
throughout. 
It is observed from Table V that the spores germinated within a rather 
restricted range of hydrogen-ion concentrations. When they were sown 
directly into the phosphate solutions, they germinated within the range 
P H 4.1 to 7.1. Presoaking before transfer appeared to enable the spores 
to germinate in more acid solutions than in the first series, for a few 
spores germinated in a solution at P H 3.6. Within the same ranges, 
also, more presoaked spores germinated than spores which were sown 
directly on the phosphate solutions. 
Table V .—The effect of hydrogen-ion concentration on the germination of spores of 
Urocystis tritici sown on phosphate solutions (A) and presoaked in distilled water 
before transfer to phosphate solutions (B ) 
Ph. 
1 
Percentage of germina¬ 
tion. 
Pa. 
Percentage of germina¬ 
tion. 
A. 
B. 
1 
A. 
B. 
3- 2 
0 
t 
O 
5-4 
27 
78 
3- 2 
O 
0 
5- 7 
38 
82 
3- 6 
0 
a Trace. 
5- 7 
45 
71 
3- 6 
0 
0 Trace. 
6. 4 
14 
12 
4. 1 
6 
22 
6.4 
11 
l6 
4. 1 
3 
34 
7- 1 
a Trace. 
O 
5- 1 
40 
92 
7- 1 
a Trace. 
O 
5- 1 
3 2 
. 85 
8-3 
0 
O 
5-4 
30 
68 
8.3 
0 
O 
° Less than i per cent; no sporidia formed. 
