BUNT, OK STINKING SMUT, OF WHEAT. 
11 
RELATION OF SOIL MOISTURE TO INFECTION. 
On April 3, 1915 a mass of dry soil was mixed with 2 per cent of its 
weight of bunt spores and moistened to saturation by adding water 
equal to 32 per cent of its dry weight. The mass was then divided 
and placed in 15 glass vessels with covers and these again placed 
inside a large moist chamber. With one exception, as long as these 
soil masses remained in the moist chamber no spore germination was 
observed. From time to time the vessels were removed from the 
chamber and allowed to dry slowly. Dates of removal and subse- 
quent appearance of sporidia are shown in Table 9. 
Table 9. — Relation of soil moisture to infection, as shown by the appearance of 
sporidia on soil masses after removal from moist chamber at Pullman, Wash., 
in 1915. 
Date re- 
moved. 
Apr. 9 
Apr. 16 
Do... 
Apr. 18 
Apr. 21 
Observation. 
Apr. 10, few sporidia. 
Apr. 14, sporidia abundant. 
Apr. 17, few sporidia. 
L Apr. 21, sporidia abundant. 
Apr. 17, sporidia abundant, dried more 
rapidly. 
Apr. 19, few sporidia, never abundant. 
Apr. 22, few sporidia, never abundant. 
Date re- 
removed 
Apr. 
Apr. 
May 
Observation. 
fApr. 27, few sporidia. 
[Apr. 28, sporidia abundant. 
No germination. 
Removed all remaining vessels to open 
air and allowed them to dry out more or 
less slowly. No germination or spo- 
ridia observed. 
The results shown in Table 9 indicate that the germination of bunt 
spores in saturated soil is inhibited and that the spores lose their 
viability in about 35 days. To obtain direct evidence as to the rela- 
tion of moisture to infection, the following experiments were under- 
taken : Sowings of 50 grains each were made in six half -gallon glazed 
earthenware pots in soil containing a known percentage of moisture. 
These pots were then hermetically closed by sealing on glass covers 
and were kept in the greenhouse. Two sets of six pots each were 
sown in March. When the wheat seedlings were in leaf they were 
transplanted to open pots, and later to the open field. Table 10 
shows the moisture content of the soil at the time of sowing as well 
as when the pots were opened for transplanting, in terms of dry soil 
and percentage of infected plants. 
Table 10. — Relation of soil moisture to bunt infection as shown by the percentages 
of bunted plants of wheat sown at Pullman, Wash., in March, 1915. 
Pot number. 
Percentage of soil 
moisture. 
Percent- 
age of 
plants 
infected. 
Pot number. 
Percentage of soil 
moisture. 
Percent- 
age of 
plants 
infected. 
1 At seed- 
ing. 
At trans- 
planting. 
At seed- j At trans- 
ing. j planting. 
Experiment A: 
No.l 
1 
J 15.8 
22.6 
26.2 
.1 30.0 
J 32.6 
.1 38. 8 
11.1 
17.6 
20.5 
25.0 
27.5 
33.3 
27.0 
31.0 
12.5 
2.3 | 


Experiment B: 
No. 1 
17.1 i 15.0 
20.0 j 
3.56 
No. 2 
No. 2 

No. 3 
No. 4 
No. 3 
No. 4 
No. 5 
No. 6 
24.2 23.4 
27.0 
5.55 
C 1 ) 

( 2 ) 
No. 5 
No. 6 
32. 27. 
37. n 39. n 
1L< 
)St. 
» All plants d 
led. 
