43 6 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
the one chance of infecting the primary or terminal bud, but also the 
numerous chances of infecting the lateral buds produced beneath the 
surface of the soil and growing out into fresh stalks. There is not only 
seedling infection, but shoot infection, and it is decidedly to the advant¬ 
age of the parasite to multiply the points of attack as much as possible/* 
If it be true that new shoots as well as the plumule are liable to infec¬ 
tion before emerging from the soil, then factors which would hasten 
growth through the soil would shorten the infection period and, there¬ 
fore, would lessen the chance of infection. Soil moisture and tempera¬ 
ture would play an important part by influencing the germination both 
of the wheat seed and of the smut spores. 
Experiments were conducted to determine the relation, if any, between 
infection and date of sowing, temperature, stage of growth prior to inocu¬ 
lation, and tillering. These experiments are discussed separately. In 
addition, experiments were conducted to determine the effects of cutting 
back inoculated plants at different periods of growth on the appearance 
of flag-smut infection. 
DATE OF SOWING AS RELATED TO INFECTION 
The following experiment was conducted cooperatively with the Mis¬ 
souri Botanical Garden, to determine if any relation existed between the 
date of sowing inoculated seed and the amount of infection produced. 
Harvest Queen was used throughout this experiment. Eleven sets of 125 
selected seeds each were inoculated and sown in rod rows at three-day or 
four-day intervals from October 17 to November 21, 1922. The rows 
were 1.5 feet apart, and the seeds were spaced at intervals of a little less 
than 2 inches. All inoculations were made simultaneously with dry, 
ground spore material of the previous season. The vials of inoculated 
seed for the later sowings were kept in a cool, dry place in order to main¬ 
tain the viability of both the spores and seed. Infection was first ob¬ 
served on April 28, 1923, on some of the plants of the first sowings. The 
dates of the various sowings are given in Table V, together with the total 
number of plants, number of infected plants, and the percentage of infec¬ 
tion for each date of sowing. 
Table V. —Percentages of infection of Harvest Queen wheat by Urocystis tritici, as 
influenced by date of seeding from October 17 to November 21, IQ22, in the Mis¬ 
souri Botanical Garden, St . Louis, Mo. a 
Date sown. j 
Total 
number. 
Number 
infected. 
Per cent 
infected. 
Oct. 17. 
21 
19 
61.3 
Oct. 20. 
48 
24 
50.0 
Oct. 24... 
37 
14 
37*8 
Oct. 27. 
26 
6 
23.1 
24 
5 
20.8 
Nov. 2. . .... . 
24 
7 
29.2 
Nov. 7. 
So 
7 
14,0 
Nov. 10. 
79 
19 
24.1 
Nov. ..... 
12 
0 
0 
Nov. 17. 
1 • 0 
72 
0 
0 
Nov. 21. 
69 
0 
0 
o Experiments in cooperation with the Missouri Botanical Garden. 
