s 
BULLETIN 1239, U. S. DEPARTMENT OF AGRICULTURE. 
favorable growth conditions may run its course within 20 daj-s. The 
exact limit is difficult to determine under field conditions because 
of the practical impossibility of knowing when the last spores 
germinated. 
PHYSIOLOGIC RESPONSE OF SPORES OF TILLETIA TO TEMPERATURE. 
Field experiments to determine the relation of temperature to bunt 
production, the condensed results of which are shown in Table 5, were 
made in the spring of 1915. Each sowing consisted of two 1-rod rows 
each of Pacific Bluestem, Early Wilbur, and Red Chaff wheat. All the 
seed was thoroughly blackened with spores of Tilletia tritici. The soil 
was well worked and in good tilth. These varieties differ widely in 
susceptibility, and these differences showed themselves consistently 
in all seedings. Table 5 shows only the averages for each date. The 
calculated mean soil temperature is based on observations by means 
of soil thermometers for the day of seeding and six days following. 
Table 5. — Results of an experiment to determine the relation of soil temperature 
to bunt production at Pullman, Wash., in 1915. 
[The experiment consisted of successive sowings in 1-rod rows of Paci^c Bluestem, Early Wilbur, and Red 
Chaff wheat. The ssed was all inoculated before sowing.] 
Date sown. 
Percentage of bunt-free and 
bunted plants. 
Bunt 
free. 
Partly 
bunted. 
Wholly 
bunted. 
Percent- 
age of 
bunted 
heads. 
Mean 
soil 
temper- 
ature 
(°C) 
Rainfall. 
Apr. 24 
Apr. 30. 
May 7.. 
May 11. 
May 15. 
May 21. 
May 25. 
May 31. 
33.49 
28.16 
46.35 
35.80 
46.01 
98.35 
98.42 
99. 16 
25. 98 
32.37 
31.57 
38.15 
27.23 
1.00 
1.24 

40.53 
39. 47 
22.08 
26. 05 
26.76 
.65 
.34 
.84 
47.44 
56. 02 
31.69 
47.87 
40.32 
1.00 
.55 
.67 
10.0 
13.3 
10. S 
13.3 
21.1 
18.3 
24. 2 
Apr. 26, 0.71 inch. 
May 8, 9, and 10, 0.90 
inch. 
May 14, 0.05 inch. 
May 17, 18, and 19, 0.41 
inch. 
On April 24 three varieties of winter wheat of medium suscepti- 
bility were sown under exactly the same conditions and in ground 
adjacent to the plats of spring wheat. These failed to head in the 
summer of 1913, and a portion survived the winter. By the following 
spring these plants were of a rather unhealthy appearance, but pro- 
duced some heads with no trace of bunt. 
Evidently all the infected plants in this experiment failed to 
survive the winter. A series of fall sowings was begun on July 28, 
1913, in which only Hybrid 143, a very susceptible variety, was used. 
The seed grain was thoroughly blackened with bunt spores. The 
plat was on a south slope where the soil, until the opening of the rainy 
season, was thoroughly dry when the earlier sowings were 4 made. As 
a consequence, it was necessary to bring the soil to good moisture 
condition by irrigation three to five days before each sowing. The 
data on mean temperature in this case cover the time from sowing to 
the appearance of the first blade and are taken from the records of a 
soil thermograph Located in the plats, with the capsule placed at the 
depth, 2 inches. 
seeding 
Each sowing consisted of 300 grams in a 
