Apr. 7,1923 Influence of Soil Temperature on Fusarium in Cabbage 63 
INFI^UENCE OF SOIE TEMPERATURE UPON THE OCCURRENCE OF THE 
FUSARIUM DISEASE IN CABBAGE SEEDLINGS 
greenhouse EXPERIMENTS 
Methods and apparatus. —^The apparatus employed for controlling 
the soil temperature in these experiments was what is termed the Wis¬ 
consin soil-temperature tank. Since it differs only in detail from that 
used by Johnson and Hartman (9) and described by Jones (jo), further 
description is considered unnecessary in this connection. A series of nine 
separate tanks or compartments was employed, with extreme tempera¬ 
tures of 14° and 38° C. and a difference of 3° between successive tanks, 
thus giving the graduated series 14°, 17°, 20°, 23°, 26°, 29^^, 3235^^, and 
38°. The temperatures below 23° were regulated by running in a small 
amount of cold water two or three times a day as the case required, while 
the temperatures from 23° to 38^ inclusive w^ere maintained through the 
use of carbon electric lamps under thermostatic control. During the 
earlier experiments some of the temperatures were regulated through the 
use of steam, but this method was abandoned when the electric lamps 
were installed. With personal attention two or three times every 24 
hours, the temperatures were kept fairly constant, rarely varying more 
than I® from that desired. 
The air temperature in the tank room w'^as kept constant wdthin a 
range of a few degrees. During the course of the first experiments it 
ranged from 18° to 22° C. with a maximum rise of 5^ to 10° for one or 
two hours on bright days. During the spring of 1919 the air temperature 
range was from 14° to 18° with a similar rise at midday on bright days. 
The surface of the soil in the receptacles was covered with a half-inch 
layer of mineral wool to insulate it from the air temperature and to 
reduce evaporation. Even with this protection, the surface inch of soil 
at the higher temperatures usually registered from i°to lower than 
the water in the tanks. However, the deeper layers of soil registered the 
same temperature as the water, and the plant roots were found to be 
distributed largely in the layers below the first inch. Therefore the 
temperatures recorded for the different series are those at which the 
water was maintained in the tanks in which the receptacles were sus¬ 
pended. 
Receptacles. —^The receptacles or culture pots were made of galvan¬ 
ized sheet iron, cylindrical, 6 inches in diameter and 10 inches deep. 
They were made ready for use by placing a layer of fine coal cinders about 
2 inches deep on the bottom with soil on top of this up to within 
inches of the top. All of the water was supplied through a glass tube 12 
mm. in diameter which was placed in the center of the receptacle of soil 
with the lower end inserted in the cinders. After the receptacles were 
filled with soil, they were so placed in the tanks that the surface of the 
soil was level with the surface of the water in the tank. They were then 
allowed to remain in the tanks one or two days before the seed was 
planted. 
Soil. —^The naturally infested soil used in all the experiments was ob¬ 
tained from a uniformly “cabbage sick” field in Kenosha County, Wis. 
It was a dark clay loam containing some gravel. Before being used the 
soil was screened and uniformly mixed with coarse sand in the ratio of 
five parts of soil to one of sand. After the sand was added, the portion 
to be used as control was autoclaved at 5 pounds pressure for two hours 
and then allowed to stand for one week before it was used. 
