6i2 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
order to allow circulation of air. The spores were tested at the beginning 
and at intervals until no germination occurred. The germination at the 
beginning was found to be 76 per cent, at the end of 3 days it was 65 per 
cent, in 5 days 50 per cent, in 10 days 35 per cent, in 13 days 15 per 
cent, in 16 days 10 per cent, in 20 days i per cent, in 23 days only a trace,, 
while in 25 days no more germination could be secured. 
No extensive work has been done to ascertain how long urediniospores 
of P. glumarum tritici mil remain viable in the field during the winter 
months. It is possible, as indicated above, to find viable urediniospores 
at almost any time during an open winter on the Pacific slope. It has 
not yet been possible, however, to learn if this is the case in the inter¬ 
mountain regions, where the winters are much more severe. Mr. A. F. 
Thiel states in a personal letter that he found, in connection with his 
studies of overwintering of stem rust in Montana, that urediniospores of 
P. glumarum were less resistant to the weather conditions than those of 
P. graminis tritici^ P, graminis avenae, P. graminis phleipratensis or P. 
triticina, 
TIME OF NATURAE INFECTION 
Stripe rust is very commonly found upon young seedlings and much 
has been made of this fact by the advocates of the theory of seed trans¬ 
mission of the disease. Experiments were arranged during the winter of 
i 9I7“I8 to ascertain how early in its development a seedling might 
become infected. Seedling plants of Chul wheat were inoculated at 
various stages in their development, beginning as soon as the plumule 
emerged and continuing with different plants at intervals until the first 
leaf was fully expanded. No infection was secured in any case where the 
inoculation was made before the primary leaf had begun to expand. 
Twenty seedlings grown from seeds germinated in Petri dishes lined with 
filter paper were used in each case. When the primary leaf was well 
expanded, these were transferred to soil in pots. 
The details of the experiment are as follows: 
No. I. —Urediniospores placed upon the plumule just as it began 
to appear. No infection resulted. 
No. 2.—When the plumule was one-half inch long, no infection 
resulted. 
No. 3.—When the plumule was i inch long, no infection. 
No. 4.—When the primary leaf was just beginning to unfold froni 
the sheath, but not well opened, 10 per cent infection. 
No. 5.—When the primary leaf was well opened, 100 per cent 
infection. 
Abundant infection has been noted upon the primary leaf of seedlings 
of Bromus marginatus, Hordeum nodosum, H, murinum, H. juhatum and 
Sitanion jubaium which came up in the rust nursery at Corvallis, Oreg.,. 
around old infected plants of the same species. (PI. II, A.) 
Uredinia appeared upon young seedlings of Chul wheat 21 days after 
it was sown on June 10, 1917, alongside of some winter wheat which was 
heavily infected with stripe rust. (PI. II, B.) Some of the same lot of 
seed was sown some distance from any known infection. No stripe 
rusC appeared on the plants from this seed until two weeks after it had 
appeared upon the seedlings mentioned above. This indicates that 
i^ection may occur under field conditions as soon as the primary leaf 
unfolds. It is very evident from observations made during the winter 
and early spring, that seedlings infected in the autumn may be a very 
