May 19,1923 
Life History of Stripe Rust 
61J 
common means of carrying the rust over winter, at least on the Pacific 
Coast. 
PERIOD OR INCUBATION 
The length of the incubation period of the uredinial stage of various 
rusts does not appear to be the same. Parker ( 8 ) found that the incuba¬ 
tion period of Puccinia graminis avenae Erikss. and Henn. and of Puccinia 
lolii avenae McAlpine, on oats, was about the same. He states, however, 
that generally, though not always, the uredinia of the stem rust appeared 
first. He took notes on the appearance of flecks on the seventh to the 
ninth day, and notes on the formation of uredinia in 12 days. He calls 
attention to the effect of temperature and light upon uredinia formation. 
Low temperatures were found to lengthen the period. Durrell and 
Parker (2) state that the incubation period for crown rust upon seedlings 
of a susceptible variety of oats averaged 7.8 days. On older plants of the 
same variety the incubation period averaged 9.5 days. Biffen (i) found 
that the incubation period of uredinia of P. glumarum on wheat was about 
10 days. Marryat (7) states that pale yellow areas appear 6 days after 
inoculation of susceptible varieties of wheat with urediniospores of P. 
glumarum. Pustules begin to appear on the eleventh and are all open 
by the thirteenth day. 
The author's observations in the greenhouse in connection with 
inoculation with urediniospores of P. glumarum tritici on wheat indicate 
that with optimum conditions for infection, namely, a susceptible host, 
fairly high temperature after the first 48 hours, good light, and vigorously 
growing seedling plants, infection begins to appear on the eighth or 
ninth day and is evidenced by lighter-colored areas on the inoculated 
portions of the leaves. Spores appear in abundance on the twelfth or 
thirteenth day. As observed by Parker { 8 ), low temperature and lack 
of sunlight may materially lengthen this period. It was observed in 
1918 in connection with inoculations which were made in the field at 
Corvallis, Oreg., late in the fall and early winter, that the incubation 
period at that time of year might be as long as 30 days. It seems possible 
that uredinial hyphae, after penetrating the host and becoming estab¬ 
lished, may lie dormant for a much longer time under conditions unfavor¬ 
able to the development of the host and then again continue growth 
and the production of spores when growth of the host is resumed. 
HEAD AND KERNED INFECTION 
A number of writers have called attention to the fact that both 
uredinial and telial infection of a number of rusts may be found upon 
the caryopses of various grains and grasses. The author (6) has sum¬ 
marized the literature regarding the occurrence of this phenomena 
and has called attention to the fact that kernels of wheat infected with 
P. graminis tritici are rather commonly found in wheat from badly 
rusted plants. The percentage of rusted kernels was not large, however, 
in any sample examined. 
The development of both uredinia and telia of P. glumarum tritici 
upon all parts of the head and kernel of certain varieties of wheat has 
been found to be very common dirring severe rust epidemics. In many 
cases of severe infection it is impossible to find a place on the entire 
plant from the surface of the ground to the tips of the awns that is not 
