474 
Journal of Agricultural Research voi. xxvn, no. 7 
Six days later they were transplanted to the containers in the tempera¬ 
ture series. At this time the first leaf of each plant was approximately 
3 inches long. 
After the seedlings were planted, waxed paper and cotton wool were 
placed over the surface of the soil to minimize evaporation until the plants 
had appeared above the soil. Although it was not possible to maintain 
equivalent and constant moisture conditions throughout the experiment, 
it is probable that the moisture content of the soil in all of the con¬ 
tainers was practically the same until just after infection had occurred. 
During the course of the experiment, the containers were weighed once 
a day and water was added to replace the losses from evaporation and 
transpiration. The moisture content throughout appeared to be adequate 
for the growth of the host plants. 
The seedlings were planted on January 18 and final observations were 
made on April 3, as by this date all uninfected plants in the three lower- 
temperature tanks had headed. The plants kept at from 29 0 to 31 0 C. 
were removed from the influence of high temperature on this date, but no 
smut developed subsequently. The results of the inoculations are given 
in Table VII, and the condition of the plants when approximately 10 
weeks old is shown in Plate 2. In estimating the percentage of smutted 
plants, all that were smutted or partly smutted are included. 
The disease appeared in plants of various ages. The first lesions were 
observed on two plants in pot 8 and in one in pot 12, 29 days after inocu¬ 
lation (PI. 1, A). The fifth leaf of both plants was heavily infected. 
It is observed that all of these plants were inoculated at 15 0 C. and were 
subsequently transferred to higher temperatures. Other plants were 
observed in which the fourth leaf contained typical lesions of the disease. 
The lesions on these plants were evident 32 days after inoculation. 
In contrast to the above, no signs of disease appeared on several plants 
in pot 1 until 84 days after inoculation. 
Table VII .—The effect of soil temperature on the development of Urocystis tritici in 
seedlings of Canberra wheat 
Pot 
No. 
Temperature. 
Inoculum. 
Amount 
infection.® 
Per cent 
infection. 
I 
H 
►H 
Presoaked spores. 
12 
TVTT 
54 * 5 
2 2 
2 
.do. 
Dry spores. 
15 
71 . 4 
21 
3 
.do. 
Germinating spores. . . . 
f! 
88. 9 
b 4 
.do. 
.do. 
« 
12 
80. 0 
5 
10—21 . 
Presoaked spores . . . 
66. 7 
I 0 
6 
.do. 
Dry spores. 
H 
52. 2 
7 
.do. 
Germinating spores.... 
1 6 
T 5 
84. 2 
f>8 
.do. 
.do. 
15 
93- 8 
To 
Remarks. 
6 plants partially 
smutted; 2 plants 
smutted at heading. 
9 plants partially 
smutted. 
3 plants partially 
smutted. 
2 plants partially 
smutted. 
6 plants partially 
smutted. 
4 plants partially 
smutted. 
3 plants partially 
smutted. 
1 plant partially 
smutted. 
a Numerator=number of plants infected: denominator^ total number of plants. 
6 Seedlings transferred to temperature series after inoculation and six days’ growth at is® C. 
