398 
Journal of Agricultural Research 
Vol. XXV, No. 9 
Comparatively few of the different varieties studied showed infection 
in the heads. This is the type of infection which is the most destructive, 
as the yield may be very materially reduced when the heads become 
infected. A discussion of this type of injury was given in one of the 
earlier papers of this series (jo). It also is noteworthy that few of 
the wheat varieties which are commonly grown in the western portion 
of the United States where stripe rust is found are very susceptible to 
the rust. Exceptions to this are several of the club varieties, Early 
Baart, Jones Fife, and a few others. 
A study of the foregoing results also will show that the varieties 
which have proved more or less resistant to leaf rust and stem rust 
have not shown, in every case, a similar resistance to stripe rust. Nota¬ 
ble examples of this are several of the durum wheats which have been 
shown to be resistant to most strains of Puccinia graminis tritici. 
Khapli (C. I. 4013), an emmer which Hayes, Parker, and Kurtzweil (6) 
found resistant to all biologic forms of stem rust thus far isolated, is not 
especially resistant to the strains of stripe rust with which it has been 
inoculated. Jenkin and Sampson (ji) state that comparatively few of 
the wheat varieties which they tested were resistant to both black rust 
(Puccinia graminis) and yellow rust (Puccinia glumarum). 
Hiltner (9, p. 83) reports that in Germany spring wheat suffers more 
than winter wheat from the attack of P. glumarum. He also states that 
the club varieties as a class appear to be especially susceptible and that 
those varieties with broad leaves were not so often attacked by the rust. 
Von Kirchner (12) gives 20.4 per cent as the average stripe-rust infection 
on winter wheat for a number of years, while spring wheat for the same 
number of years showed only 16.2 per cent infection. Jenkin and 
Sampson (11) state that autumn varieties were found to be more sus¬ 
ceptible to black rust and the spring varieties to yellow rust. Schneider- 
han, in the unpublished report of the Sherman County Branch Station, 
Moro, Oreg., for 1916, reports that when certain varieties were grown as 
both spring and winter wheats, those sown in the fall developed the 
larger percentages of infection of stripe rust. 
Examination of Tables III and IV shows that leaf infection in the 
seedling stage usually was much greater in spring-sown wheat. Infection 
at heading time, on the contrary, was in most cases much greater in 
winter wheat. It seems reasonable to suppose that both seasonal and 
regional differences in climate will determine to a certain extent whether 
fall-sown or spring-sown wheat becomes more heavily infected with 
stripe rust. 
Histological studies of resistant and susceptible varieties of wheat 
attacked by stripe rust have not been made. The general external 
macroscopic evidences of resistance appear to be similar to those 
described by Stakman (17) for Puccinia graminis tritici E. and H. and 
by Parker (13) for Puccinia graminis avenae E. and H. Plates 3 to 5 
illustrate the typical effect of P. glumarum tritici upon resistant hosts. 
Large areas of killed tissue develop on the portions of the leaves inocu¬ 
lated, followed by the production of very few if any uredinia. Upon 
varieties which are moderately resistant, urediniospores often are pro¬ 
duced in abundance but no spread of the rust occurs from the parts of 
the leaf inoculated, and these portions are soon killed. 
