Apr. 7,1923 Influeyice of Soil Temperature on Fusarium in Cabbage 73 
Here again, all three of the Commercial Hollander plants developed 
typical yellows at 23^ to 29°, inclusive, whereas only one or two of the 
Wisconsin Hollander plants showed any symptoms of the disease at all 
and then only in incipient form in the lower leaves. The number of 
plants is too small to warrant definite conclusions, but the evidence 
from both field and greenhouse experiments seems sufficient to indicate 
that older plants are more resistant than younger ones, and also that 
resistance becomes more stable as the plants grow older. There is also 
some indication here that resistance was weakened by starting the 
plants at a higher temperature, but the experiment needs to be repeated 
with larger numbers of plants before final conclusions on this point are 
justified. 
The fact that a higher percentage of yellows develops at tempera¬ 
tures unfavorable for the growth of the seedlings is further evidence 
that the resistance is “broken down’' at these temperatures. It has 
been reported that hereditary characters in several different organisms 
have been modified by changing the environment (including tempera¬ 
ture) of the individuals. Baur (j, p. 8 -g) found that flower color, an 
inherited character of the Chinese primrose {Primula sinensis rubra) y 
was conditioned upon temperature. The plants were grown by the 
usual method until about one week before the blossoming stage; then 
some of them were put into a warm room (30® to 35° C.) and the others 
into a cool room (16^ to 20°.) The plants at the higher temperature 
produced pure white flowers, while those at the lower temperature pro¬ 
duced flowers of the normal red color of the variety. Biffen (4), in his 
work on the inheritance of resistance to yellow rust in wheat, concluded 
that any factor altering in any way the metabolic processes of the plant 
in turn alters the degree to whidi it is attacked by yellow rust and 
probably other fungi as well. He also found that a variety of wheat 
which under ordinary conditions of cultivation would be classed as mod¬ 
erately susceptible may be severely attacked when large amounts of 
nitrates are added to the soil. 
/ FIELD EXPERIMENTS 
FIELD OBSERVATIONS 
Jones and Gilman (ii) first recorded the fact that severe attacks of 
cabbage yellows are associated with hot, dry weather. Gilman (<?) 
analyzed this evidence in detail and showed that the incubation period 
of the disease under field conditions is also materially influenced by 
soil temperature. The incubation period was about 14 days in 1912 
when the mean daily temperature 6 inches below the surface was about 
23® C. and 20 days in 1914 when the mean daily temperature at the 
same depth was about 20°. 
Similar observations were made during the summers of 1917 and 1919 
in the same field by the writer. In 1919 the mean daily soil tempera¬ 
ture 4 inches below the surface was 25° C. at the time of transplantation. 
Thirteen days later 30 per cent of the Commercial Hollander plants 
showed typical yellows. This high percentage of diseased plants, 
together with the different stages of symptoms at that time, indicated 
that the disease had been present in some of the plants at an earlier 
date. According to these observations, the incubation period of the 
disease may vary under field conditions from about 12 days with a 
