RUST RESISTANCE IN WINTER-WHEAT VARIETIES. 25 
under various temperature conditions and at various stages of 
development of the plant. The work has been done by different 
persons at different agricultural experiment stations and always 
with the same results. The only visible evidence of infection in 
the seedling stage has been the occasional appearance of very indefi- - 
nite, scarcely visible, whitish flecks, generally less than 0.1 millimeter 
in diameter. These indefinite flecks are not similar to the areas or 
flecks occurring on the seedlings of the resistant emmers and durums 
(Pl. XI, fig. 2, C) and are very much less conspicuous. In this 
respect Piece Tapes varieties of winter wheat are distinct in their 
behavior. 
The behavior of Kanred, P1066, ane P1068 in the nursery and 
field is not greatly different from hah | in the greenhouse. Table 1 
shows that these varieties had very low percentages of stem-rust 
infection, varying in 1916 and 1917 from a trace to 10 per cent. 
In 1915 the percentages recorded were higher. In view of present 
knowledge of the existence of several distinct biologic strains of 
wheat-stem rusts (38, 39, 40, 41), this rather heavy infection very 
probably was due to the use of one or more biologic strains of stem 
rust similar to, if not identical with, the one recently described by the 
writers (30). 
When mature culms of the three resistant varieties were inoculated 
in the greenhouse with cultures of Puccinia graminis tritici, a response 
on the part of the host to the rust infection was only occasionally 
visible. Slightly yellowish or brownish white minute dead areas 
were sometimes vaguely visible, indicating that infection had. 
occurred but that the organism had ceased to develop. 
The results reported in this bulletin establish the fact that Kanred 
and two other very similar pure lines of hard red winter wheat are 
resistant to certain biologic strains of black stem rust. 
More recent studies (25, 30, 41) have shown that these varieties 
are not resistant to all the known strains of stem rust. Extensive 
field observations made in 1919 and 1920 have indicated, however, 
that Kanred is much less severely injured by most of the stem-rust 
strains occurring in Kansas than are Turkey and Kharkof, the other 
varieties commonly grown. Reports from Wisconsin, Alabama, 
Nebraska, New York, Illinois, Missouri, Iowa, California, and New 
South Wales (Australia) indicate that these three varieties have 
shown resistance to stem rust, while the Minnesota and the South 
Dakota agricultural experiment stations report them rather severely 
rusted, although in South Dakota Kanred showed less rust than 
Turkey. Because of the existence of distinct strains of stem rust 
it is probable that the behavior of these varieties will vary in different 
seasons and in various sections of the country. 
