Feb. 16, 1924 
Flag Smut 0} Wheat 
475 
Table VII .—The effect of soil temperature on the development of Urocystis tritici in 
seedlings of Canberra wheat —Continued 
Pot 
No. 
Temperature. 
j 
Inoculum. 
Amount j Per cent 
iniection.oj infection. 
Remarks. 
°c. 
9 
j 24-26 . 
Presoaked spores. 
fV 
17. 6 
2 plants partially 
smutted. 
10 
.do. 
Dry spores... 
JL 
O C 
11 
.do. 
Germinating spores.... 
5 
TT 
y- h 
29.4 
1 plant partially 
j N 
smutted. 
b j 2 
.do. 
JL 
13 
29-31 . 
Presoaked spores . 
16 
D u * 6 
0 
14 
.do. 
Dry spores... 
14 
0 
0 
15 
.do. 
Germinating spores.... 
tst 
A 
0 
& 16 1 
1 
! 
i. do . 
! 
.do. 
A 
7 - 7 
° Numerator=number of plants infected; denominator=total number of plants. 
6 Seedlings transferred to temperature series after inoculation and six days’ growth at 15 0 C. 
Occasionally signs of disease were visible on younger tiller shoots be¬ 
fore any lesions appeared on the main shoot. Instances occurred on two 
plants in the 14 0 to 16 0 C. series in pot 1, in which presoaked spores had 
been used as inoculum. 
In considering the effect of temperature on the development of the 
disease, it would appear from Table VII that the heaviest infection oc¬ 
curred in the series kept at from 14 0 to 16 0 C. and 19 0 to 21 0 . This is 
apparent whether the inoculations are made with ungerminated or with 
germinated spores. On this basis alone, there are no significant differ¬ 
ences between the results from either of these series. However, judged 
on the date of the first appearance of the disease and the degree of infec¬ 
tion produced in the plant, the series at 19 0 to 21 0 more closely ap¬ 
proaches the optimum conditions for infection and subsequent develop¬ 
ment of the smut (PI. 2). 
The most severe infections recorded in the experiment occurred in 
pots 7 and 8. In these cases, germinating spores were used as inoculum. 
Practically all the plants were completely affected and the disease ap¬ 
peared in all such plants approximately six weeks from date of inocula¬ 
tion. Plants inoculated with germinating spores consistently became 
more heavily infected than those inoculated with ungerminated spores. 
In the lower temperature series there was a higher percentage of par¬ 
tially smutted plants and in the majority of instances the first appear¬ 
ance of the disease was considerably later than that recorded for the 
series at 19 0 to 21 0 C. 
An effort was made to determine if inoculation at low temperature 
and subsequent transference of the inoculated plants to higher tempera¬ 
tures would favor the development of the disease. The plants in pots 4, 
8, 12, and 16 were inoculated at 15 0 C. and then transferred to various 
temperature tanks, as previously described. There apparently are no sig¬ 
nificant differences between the amount of infection at 14 0 to 16 0 and at 
19 0 to 21 0 , although the highest recorded infection, 93 per cent in pot 
8, and the earliest recorded infections, two plants in pot 8 and one plant 
in pot 12, occurred in the transferred plants. 
In the higher temperature series, the transferred plants were much 
more heavily infected than the plants which had been exposed to con¬ 
stant temperature throughout. In the series at 29 0 to 31 0 C., the only 
