Feb. x6,1924 
Physiological Studies on Flag Smut of Wheat 
443 
4, and 34 days earlier than in row 1. Row 3 had a final infection per¬ 
centage of 58.3 in comparison with 31.3 per cent in the control row. There 
was one plant in row 1 which was cut back twice before infection was 
noted—once in the two-leaf stage, and again after the plant had headed. 
Finally a small secondary infected shoot was put out from the first node 
above ground. 
Table IX.—Percentages of infected plants in eight wheat varieties inoculated with Uro- 
cystis tritici , and cut back at various stages of growth, in the greenhouse at Arlington 
Experiment Farm, Rosslyn, Va., in IQ21-22 
I Row number and stage when cut 
back. 
Control. 
Variety. 
| C.I. No. 
j 
i 
1 
Two-leaf. 
| 
1 2 
Time of 
normal 
infection. 
3 
Heading. 
4 
Not cut. 
Bunyip. 
| 
5 ° 12 
40.0 
40.0 
5 8-3 
31-3 
Comeback. 
4991 
90.9 
72.7 
84.6 
a 20.0 
Florence. 
5 i 2 9 
50.0 
5 °.° 
60.0 
3 1 - 6 
Sonora. ! 
4293 
36.3 
23.0 
22.2 
25.0 
Pacific Bluestem. i 
3019-3 
83-3 
43-7 
42.8 
33-3 
Flint.| 
6612 
54-5 
26.6 
41.2 
Fultz. j 
3598 
40.0 
77-7 
13*3 
18.8 
Jones Fife... .j 
1 
5608 
64.2 
44.4 
46.6 
42.9 
® Normal infection. An additional 73.3 per cent of the plants showed infection in small secondary shoots 
which appeared after the first culms had matured. 
A striking difference in infection percentages was shown in the various 
rows of Comeback. It will be noticed from figure i that by the time 
there was 72.7 per cent of infection in row 1 there was 15.3 per cent in 
row 3, 9 per cent in row 2, and 20 per cent in row 4. None of the plants 
in rows 2, 3, and 4 had been cut back at this time. After all infected 
plants had been removed from the four rows the remaining sound plants 
in row 2 were cut the same day. Row 3 was cut back about one month 
later. Small shoots soon were produced at the crown and nodes, and 
many of these were infected with flag-smut sori. The dotted line in 
row 4, or the control, represents the infections which appeared in the 
small secondary shoots which were produced after the culms were prac¬ 
tically mature. 
Row 1, sown to Florence, produced 18.4 per cent more smut than the 
control, and the period of smut maturation was reduced by 30 days. 
Sixty per cent of the plants in row 3 were infected. This was the maxi¬ 
mum for this variety, and exceeded by 28.4 per cent the infection recorded 
for the control row. 
The final percentages of infection for Sonora did not show great differ¬ 
ences. Row 1 produced 36.3 per cent, or 11.3 per cent more infection 
than developed in the control row. Row 2 contained 23.0 per cent of 
infection in comparison with 25.0 per cent in the control, but it should be 
noted that the total percentage of smut recorded for row 2 had developed 
22 days before infection appeared in row 4, and 73 days before the last 
infected plant was noted in row 4. Although row 1 showed the highest 
percentage of infection, no lesions appeared in row 1 until 13 days after 
