28 BULLETIN 1046, U. S. DEPARTMENT OF AGRICULTURE. 
(5) Several varieties of sprmg wheat proved rust resistant under 
the conditions of these experiments, though the Black Persian was 
the only spring-wheat variety of the common or bread-wheat group 
(Triticum vulgare) which was found to be resistant. Of the varieties 
of durum or macaroni wheat (Triticum durum), Beloturka (C. I. No. 
1518), Iumillo (C. I. No. 1736), Kubanka (C. I. No. 2094), Monad 
(D-1), and Pentad (D-5) showed definite signs of resistance to stem 
rust. A hybrid of Iumillo x Preston, resembling the durum parent, 
also was found to be rust resistant. All of the strains of emmer and 
einkorn grown gave some evidence of resistance. 
(6) In the greenhouse experiments the plants were studied for 
rust resistance at two stages of growth, viz, as seedlings and at the 
time of heading. The results were very similar to those in the field 
experiments. All the winter-wheat varieties were susceptible except 
three—Kanred, P1066, and P1068. Kansas No. 2390, which ap- 
peared to be somewhat resistant in the field, showed no evidence of 
resistance at either stage of growth in the greenhouse. Most of the 
-spring-wheat varieties which the field experiments had shown to be 
resistant also gave more or less evidence of resistance under green- 
house conditions. This was not true, however, of einkorn. 
(7) Although the results obtained in the field and those in the 
greenhouse agree fairly well, final conclusions as to rust resistance of a 
variety should not be drawn from greenhouse tests alone. The com- 
bined evidence from nursery experiments and inoculations of seed- 
lings and of plants in the heading stage under greenhouse conditions 
is much more likely to agree with actual field trials, which must 
always be the final test of the practical value of any variety. 
_ (8) The behavior of the rust parasite on the inoculated plants of 
the three resistant varieties—Kanred, P1066, and P1068—seems to be 
- different from that in other varieties described as resistant. In most 
other varieties prominent flecks are nearly always present in 8 to 12 
days after inoculation, and most frequently small uredinia are pro- 
duced. In these three varieties, however, flecks are very rarely 
visible, and in no instance have even the most minute uredinia been 
observed. 
(9) Reports from Alabama. California, Illinois, Iowa, Missouri, 
Nebraska, New York, Wisconsin, and New South Wales indicate 
that these three varieties are resistant to stem rust; but Minnesota 
and South Dakota report them rather severely attacked by stem rust. 
The occurrence of distinct strains of stem rust complicates the prob- 
lem of predicting what their behavior may be during different seasons. 
Present knowledge of the distribution of stem-rust strains and whether 
they occur each season in definite regions is so limited that the resist- 
ance or susceptibility of these wheats in any region may differ from — 
season to season. 
