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RUST RESISTANCE IN WINTER-WHEAT VARIETIES. 23 
1526) and Khapli emmer (C. I. No. 4013) seemed to show more con- 
sistently the type designated as R,. Khapli emmer (C. I. No. 4013) 
is the only variety of spring wheat so far studied that under all 
conditions seemed to exhibit a high degree of resistance in the field 
and in the greenhouse. Even this variety, however, may be classed 
at times as R, instead of R,. The seedlings of the so-called wild 
wheat of Palestine, Triticum hermonis Cook (C. I. No. 3109), really 
a form of emmer, all proved to be susceptible. 
The purple color mentioned under “‘Remarks”’ occurred in some 
varieties and surrounded the uredinia. It does not appear con- 
sistently in any one variety. Environmental conditions seem to 
affect its production. 
COMPARISON OF NURSERY AND GREENHOUSE RESULTS. 
In general, the results of thé greenhouse inoculations were similar 
to those produced under field conditions in the rust nursery. All of 
the winter-wheat varieties were found to be susceptible except 
Kanred, P1066, and P1068. Kansas No. 2390, which appeared to be 
partially resistant in the rust nursery, gave no evidence of being 
resistant in the greenhouse. 
In the nursery, results on rust behavior usually are obtained on 
varieties in the heading stage, but in the greenhouse the seedling 
stage is most commonly used. Determining the resistance of varie- 
ties as seedlings is the most convenient method, particularly when a 
number of distinct biologic strains of rust are being used. It perhaps 
is the most severe test that can be given a variety and should always 
serve as a check on nursery results. The results thus obtained, 
however, scarcely can be considered as the sole criteria of the actual 
field resistance or susceptibility of a variety; in fact, plants showing 
certain effects when inoculated in the seedling stage in the green- 
house may respond very differently to the same rust when they are 
subjected to it in the heading stage under field conditions. No 
definite statements as to the cause of these differences can be made 
at this time. The same factors causing resistance or susceptibility 
may operate in all stages of growth, but the reaction of the host and 
parasite at various stages of development may be different. 
It is possible that time of maturity may have an important 
influence on the extent of the rust on a given variety, but if the rust 
is epidemic before the plants reach the heading stage there can be 
no doubt as to the plants having been exposed to infection. The 
differences perhaps are due to complex factors in the developmental - 
stages in a variety, which may cause a different response to rust 
infection. To whatever cause these differences in behavior in the 
seedling and heading stages may be due, the behavior of any variety 
