Sept. 1, 1924 
223 
Stripe Bust 
and with the development of new 
leaves the grass plants also became 
heavily infected. From the foregoing, 
it would appear that viable uredinio- 
spores from one or both of the grasses 
had found lodgment on the leaves of 
the nearby wheat plants, and that the 
subsequent infection of the latter was 
traceable to spores produced in the 
grass hosts. 
Rostrup {20, p. 260) is of the 
opinion that the stripe-rust fungus 
hibernates as living mycelium, and 
that on resumption of growth is follow¬ 
ed promptly by the development of 
uredinia. Apparently the temperature 
permitting such renewed activity is 
relatively low, for, as pointed out by 
Henning and Bygden ( 9 ), stripe rust 
not uncommonly appears shortly fol¬ 
lowing the melting of the snow. In 
Denmark it was more or less prevalent 
in April of 1906, 1910, 1911, and 1914. 
In 1910 a new crop of urediniospores 
sufficiently mature to germinate was 
found as early as the first week of 
March. 
Klebahn {14) tried to show by experi¬ 
ment the hibernating capacity of the 
urediniospores of Puccinia glumarum, 
but obtained only negative results. He 
was successful, however, in securing 
germination of urediniospores of P. 
dispersa Erikss. and Henn. that had 
survived the winter. Hecke (7, 8) 
studied the same problem in Austria 
and showed that the mycelium of P. 
glumarum could endure a temperature 
of —10° C., or lower. He further 
pointed out what is probably a fact, 
namely, that the mycelium of this rust 
organism will survive such winter con¬ 
ditions as may not prove too rigorous 
for the host. 
K. Murashkinski, Director of the 
Western Siberian Laboratory of the 
Siberian Agricultural Academy, Omsk, 
Siberia, in correspondence with the 
senior writer, states that he had locally 
observed Puccinia glumarum on Bromus 
unioloides H. B. K. and Elymus dahuri- 
cus Turcz. in 1920 and 1921, and that 
infection seemed to be confined solely 
to these two grasses. Omsk is situated 
in latitude 55° N. and is subject to 
extremely low winter temperatures. 
The moderately heavy and continuous 
snow cover of that region from October 
until April, however, undoubtedly 
affords ample protection to both host 
and parasite, thus insuring the propa¬ 
gation of the rust organism by means 
of hibernating mycelium. 
CLIMATE IN RELATION TO DEVEL¬ 
OPMENT OF STRIPE RUST 
Unpublished meteorologic data fur¬ 
nished by D. E. Stephens, 4 for the 
period September, 1914, to September, 
1915, inclusive, would seem to indicate 
beyond doubt the nice dependence of 
Puccinia glumarum on climatic condi¬ 
tions. During May and June, 1915, 
stripe rust developed at the substation 
to the point of a genuine epidemic. 
Given the necessary inoculum to insure 
a general distribution of seedling infec¬ 
tion during September and October, 
1914, the heavy and almost continuous 
snow cover of the winter of 1914-15 
furnished ideal overwintering condi¬ 
tions. Reference to Table II will show 
how favorable for infection were the 
precipitation and temperature condi¬ 
tions of September and October, 1914. 
It will be noted also that these same 
factors during the spring and early 
summer months of 1915 were such as 
to promote the further development 
and spread of the rust. If these data 
are compared with those for September 
and October, 1915, and those of the 
spring and early summer months of 
1916, it will be noted that the factors 
favoring early emergence and normal 
subsequent fall growth of volunteer 
wheat were quite as ideal during Sep¬ 
tember and October, 1915, as they 
were during the same period in 1914. 
Moreover, assuming that the 1915 epi¬ 
demic had its origin in hibernating 
mycelium arising from infection during 
the autumn of 1914, the amount of 
available rust inoculum (uredinio¬ 
spores) must have been very much 
more abundant than in the fall of 1914. 
It also should be noted that the winter 
of 1915-16 was characterized by a 
nearly continuous snow cover. The 
temperature and moisture conditions 
of March, April, and May, 1916, were 
not inimical to the development of 
stripe rust, yet 1916 was not a rust 
year. Commercial wheat fields in¬ 
spected in June showed but a trace 
and only the more susceptible varieties 
growing on the station farm were 
infected. 
4 Stephens, b. E — report of the sherman county branch station, moro, Oregon, 1914-16 . 
[Unpublished. Copies in Office of Cereal Investigations, U. S. Dept. Agr., Washington, I). C.] (C. E. 
Hill, joint author, 1915-16.) 
