552 
Journal of Agricultural Research voi. xxvm, No. 6 
dry weather whereas in moist summers the disease often caused little damage, 
even when a large part of the plants were infected. 
While Ilavn’s observations seem clearly to justify his conclusions that, under 
the soil conditions prevailing in Danish fields, soil drainage, along with soil 
reaction, plays an important part, yet he gives no exact or experimental data 
upon which to base comparisons. He did not carry out any experiments to 
determine definitely the influence of water content apart from the other factors 
connected with poor drainage. While he follows the common habit of speaking 
of low or poorly drained soils as “cold,” we have no data on the possible influence 
of soil temperature as a factor in relation to clubroot infection or development. 
It seemed, therefore, worth while to attempt to segregate and define more clearly 
the possible influence of each soil temperature and soil moisture on this disease. 
METHODS 
Unless otherwise stated under the individual experiments, the method of 
procedure was in general as outlined below. In most of this work two distinct 
types of infested soil were used, both being in good physical condition and of 
high fertility. These will be designated throughout as A and B. Soil A was a 
clay loam obtained from a small home garden located at Chatham, N. J., where 
the disease had become serious and widespread. Soil B was a sandy loam, rich 
in organic matter, taken from a badly diseased portion of a commercial cabbage 
field near Kenosha, Wis. The water-holding capacity was determined for each 
soil by means of the usual 12-inch brass cylinder method. For comparison with 
these determinations the moisture equivalents were determined by means of the 
method described by Briggs and McLane (2 ), that is, by using a centrifuge with 
a radius of six inches and a speed of 2,400 revolutions per minute for 40 minutes. 
The wilting coefficient for each soil was calculated by means of the indirect 
method based on the moisture equivalent as described by Briggs and Shantz 
(5). The following is a summary of these determinations: 
Water-holding capacity, moisture equivalent, and wilting equivalent of the clubroot 
infested soils 
Soil 
Water¬ 
holding 
capacity 
Moisture 
equiva¬ 
lent 
Wilting 
coeffi¬ 
cient 
A . 
Per cent 
45 
62 
Per cent 
24 
34 
Per cent 
13 
19 
B____ 
To insure vigorous growth of plants the fertility of the soil was in each case 
increased by adding powdered potassium nitrate and dicalcium phosphate at 
the rate of 1 gm. of each chemical for every 3 kgm. of soil. Each lot was sifted 
through a 3-mm. sieve and the water content determined. Cans of equal weight 
were selected, and an equal weight of soil was put into each one so that when 
packed and planted the surface was about 1 inch below the top of the can. In 
order to make provision for water and aeration an inverted 3-inch flower pot 
connected with the surface by a glass tube was placed near the center of each 
can. When the soil was mixed, the water content was a little above that desired 
as the lowest moisture content to be maintained in the series. When a given 
series was repeated, the same soil was sifted, mixed, and replaced in the cans. 
In all this work seedling cabbage plants were used. These were grown in 
sterilized soil and transplanted to 3-inch pots where they were allowed to grow 
for from three to eight weeks in a greenhouse maintained at a temperature 
