462 
Journal of Agricultural Research vot xxiii, no. 6 
There is considerable variation from year to year, but the varieties 
generally maintain their relative positions. The four resistant ones are 
always comparatively resistant and the susceptible ones are always 
comparatively susceptible, regardless of seasonal fluctuations. Turkey, 
representing the extreme resistant type, and Fife, representing the 
extreme susceptible type, show less variation than the others. Marquis 
shows less variation than any of the others during the three years recorded 
and is so uniformly resistant that farmers often take advantage of it and 
do not treat the seed before planting. It was a matter of considerable 
surprise, therefore, when it was discovered that Marquis was susceptible 
when planted in the fall. In 1919 a fall sown row of inoculated seed 
produced 661 heads, 489, or 74 per cent, of which were bunted. The 
same phenomenon was observed in 1920, the 14 plants that survived the 
winter producing 31 per cent bunt, compared with 3.5 per cent produced 
from a spring planting of 90 plants in the same field. The record of 
Florence, the other spring wheat, is taken from fall sowings but is some¬ 
what more resistant when spring-sown. Evidently the resistance of 
Marquis is different from that of the others, inasmuch as it is neutralized 
by the lowered temperature or the winter rest period. There seems to 
be no peculiar habit of growth or taxonomic difference associated with 
this loss in resistance, but it is a constantly recurrent phenomenon 
obtaining wherever tested. An example of the uniformity of these 
reactions is shown in the records from Davis, Calif. Seed of the three 
varieties Turkey, Florence, and Marquis was sent to that Station to 
be tested for bunt resistance in the season of 1920. Plantings of each were 
made November 4 and December 21, 1919. More than a thousand heads 
of each were produced in 1920, of which Marquis contained 37 per cent 
of bunt heads, Turkey and Florence containing but 7 and 6 per cent, 
respectively. The spring sowing of Marquis was uniformly resistant. 
This does not mean that all the others have the same kind of resist¬ 
ance. In fact they have not, according to the segregation tests of their 
hybrid progeny, as will be shown later. It seems probable, from a 
study of Table III, that the different wheats do not react the same to 
climatic influences from year to year. For example, in 1920 the re¬ 
sistant varieties (with the exception of Marquis) produced more than 
twice as much bunt as their 3-year average shows, while the four sus¬ 
ceptible varieties produced an average of 7.8 per cent less in a similar 
comparison. The reverse condition obtained in 1916, while in 1918 
all varieties produced less than normal, and in 1919 all but Turkey 
and Alaska produced more than normal. It is very evident that a 
“good” or “bad” smut year does not apply equally to all varieties. 
The percentage of bunt produced on the partly bunted plants was 
much less on the resistant than on the susceptible varieties, the ratio 
being 25 to 67 when the four resistant varieties of Table III are com¬ 
pared with the four susceptible ones. This may be taken as an argu¬ 
ment in favor of the physico-chemical nature of resistance, for here 
there can be no question about the plants being infected. The difference 
is plainly one of greater incompatibility of the resistant hosts. The 
ratio of total bunt 4.5 to 75.9, however, shows a much stronger contrast 
and is the just and proper ope to use as a quantitative measure of re¬ 
sistance or susceptibility. 
