Feb. io, 1923 
Genetics of Bunt Resistance in Wheat 
459 
in the other, the coefficient of correlation equals o. Table II presents 
such a correlation. 
Tabi,F II .—Correlation of 150 varieties of wheat in respect to hunt resistance 1 
1 Percentage of bunt at Moro, subject; percentage of bunt at Pullman, relative; 1919. 
Coefficient of correlation~o.654io.0315. 
A comparison of 150 selections of wheat (mostly Triticum vulgare, a 
few being club and durum) tested at Pullman, Wash., and Moro, Oreg., 
show a correlation coefficient, according to Table II, of 0.654 ± 0.03 1 5. 
Moro has an arid climate with an average rainfall of 11.6 inches. The 
elevation is 1,800 feet; the soil, a fine silt loam. Pullman has an annual 
rainfall of 21 inches, a clay loam soil, an elevation of 2,500 feet, and a 
lower summer temperature than Moro. The Moro data were obtained by 
counting the heads of bunt and wheat from which the percentages were 
figured. The Pullman figures were obtained by the combination plant 
and head count described on page 460. Taking into account the differences 
in climate and methods, the high correlation is significant. It shows that 
resistance and susceptibility are fundamental differences and are not 
easily changed by environmental conditions. A large number of these 
varieties have been tested at Davis, Calif., Aberdeen, Idaho, and Cor¬ 
vallis, Oreg., under wide differences of soil and climate, and the indications 
are that the common varieties that are decidedly resistant or susceptible 
are outstanding in those respects at all places where tested. Table II 
shows only four varieties less than 10 per cent bunt at both Stations, but 
30 varieties more than 90 per cent susceptible. The average of all 
varieties at both Stations is 70 per cent, which is very near tie figure 
given for the T . vulgare group in Table I, in which a much larger number 
of varieties is represented, covering the two-year test (1919 and 1920) at 
Pullman. 
It is very seldom that a row of wheat, containing, say, from 50 to 100 
plants produces nothing but bunt heads, no matter how susceptible the 
variety is or how favorable the conditions for infection are. A small 
number of wheat heads, and usually a few plants, escape the fungus and 
produce normal seed. It might be assumed that these occasional plants 
were resistant mutants. To test this possibility 10 bunt-free plants of 
hybrid 143 were selected in 1913, and for three years smut-free plants 
from the most resistant row were selected. At the end of the third year 
the selected plants produced 85 per cent of bunt as compared with 80 
