Feb . 16,1924 
Physiological Studies on Flag Smut of Wheat 
433 
recovered from the soil by fractional centrifuging. The heavier soil 
particles with many spores were centrifuged out first and then a 
layer, consisting of many spores and the lighter soil particles, was ob¬ 
tained. To test spore germination, this layer was pipetted off into a 
Syracuse watch glass, tap water added, and the whole placed in an in¬ 
cubator at 18 0 C. But it had been found that flag-smut spores often fail 
to germinate in cultures, although spores from the same source produced 
abundant infection in susceptible plants inoculated with them. So it 
was decided to grow seedlings in the heavier residue to determine the 
viability of these overwintered spores by their infective power. Five 
seeds of wheat were sown in each soil and spore residuum and allowed to 
grow in the same chamber with the spore germination tests. Harvest 
Queen was sown in the series dug up on November 1 and November 28, 
while in the series dug on April 10, 1922, both Harvest Queen and Bobs 
were sown. 
When these seeds had germinated and each plant had one well-developed 
leaf, they were transplanted to clean soil in die greenhouse. Infection in 
the earlier sowings was first observed in January, and the final results 
were recorded in June. These data, together with the results of the 
spore germination tests, are recorded in Table III. 
Table III .—Viability and infective power of spores of Urocystis tritici buried for varying 
periods in different types of soil at Granite City, III., on October 6 , IQ21 
Dates baskets were dug from soil. 
Soil and inoculum. 
Depth 
Nov. i, 1931 
(Series i). 
Nov. 38, 1931 
(Series 2). 
Apr. 10, 1922 
(Series 3). 
u 
burial. 
Spore 
germi¬ 
nation. 
Infec¬ 
tion on 
Har¬ 
vest 
Queen. 
Spore 
germi¬ 
nation. 
Infec¬ 
tion on 
Har¬ 
vest 
Queen. 
Spore 
germi¬ 
nation. 
Infec¬ 
tion on 
Har¬ 
vest 
Queen. 
Infec¬ 
tion on 
Bobs. 
Black alluvial soil plus spores. 
Inches. 
0- 2 
Per ct. 
40.0 
+ 
Per ct. 
O 
_ 
Per ct. 
O 
Per ct. 
0 
Do. 
2- 4 
— 
O 
+ j 
O 
— 
O 
0 
Do. 
4- 6 
— 
75 *o 
_ 
O 
— 
0 
0 
Do. 
6- 8 
— 
75 *o 
— 
O 
— 
O 
O 
Do. 
8-10 
— 
50.0 
— 
O 
— 
0 
0 
Black alluvial soil plus in- 
infected leaves. 
0- 2 
_L 
0 
j + 
1 
O 
| 
1 — 
O 
O 
Do. 
2- 4 
— 
0 
+ 
i ° 
— 
O 
20 
Do. 
4- 6 
+ 
40.0 
+ 
O 
— 
O 
O 
Do. 
6- 8 
+ 
0 
0 
— 
O 
20 
Do. 
8-10 
— 
0 
! + 
O 
+ 
O 
O 
Basaltic soil plus spores. 
4 " 5 
— 
33*3 
1 - 
O 
— 
O 
O 
Basaltic soil plus leaves. 
4 - 5 
— 
40.0 
j + 
20 
O 
0 
Sandy loam plus spores. 
4 “ 5 
+ 
30.0 
1 
O 
I 
j 
| - 
O 
0 
Sandy loam plus leaves. 
4 - 5 
0 
t 
1 
f 
1 ° 
j 
O 
O 
The foregoing results seem to indicate that the infective power of the 
spores was markedly decreased during the time between the removal 
of the first and second series, or between November 1 and 28. The spore 
germinations show a slight increase, due probably to a difference in the 
method of germination. The two cases of infection obtained in Series 3 
from spores buried over five months were noted on Bobs, a very sus¬ 
ceptible spring wheat which had not been used for the earlier tests. 
