1916] 
GILMAN—CABBAGE YELLOWS 65 
house. The yellows appeared in the warmer house on De- 
cember 29. Each of the seedlings showing the symptoms of 
the disease was sterilized by placing the entire seedling in hy- 
drogen peroxide and washing in sterile water. It was then 
placed on potato hard agar. The fungus grew readily from 
the stem of the infected seedlings, as is shown in pl. 2, figs. 
8-1. The flats of infected soil were interchanged, and 
after replanting on January 29, the results were found to be 
the same; that is, the plants in the warmer house showed the 
disease, while those in the cooler house remained healthy. The 
first disease symptoms were observed on February 10. 
During the above experiments the temperatures were as 
constant as they could be made in a greenhouse where the 
steam supply was regulated by means of an automatic thermo- 
regulator. Of course, the heat on very sunny days was much 
greater than desired, but this factor could not be controlled, 
as shading caused too rapid elongation of the plants and a 
consequent susceptibility to damping off. It was found, how- 
ever, that the soil temperatures were fairly constant, being 
from 23 to 26°C. in the warmer house and from 12 to 16°C. in 
the cooler house. These determinations were made directly by 
placing the thermometer bulb two inches below the surface 
of the soil and after the mercury had come to rest making 
the reading. 
In one experiment the number of plants used in the trial 
was noted, and the percentage diseased after an exposure of 
three weeks calculated from actual count. The experiment 
was started January 29, 1914. The trial consisted of seven 
pots of infected soil, and two pots of normal greenhouse 
soil for controls. Five pots of infected soil were placed in 
the warmer greenhouse and two in the cooler house. One pot 
of the normal greenhouse soil was placed in each house. The 
disease was found first on February 10, and the plants were 
pulled and counts made on February 21. If the experiment 
had been continued, doubtless all the plants in the warmer 
house would have been destroyed, as they had been in the 
other experiments. Table xr gives the results. 
5 
