May 10,1924 Effect of Soil Temperature and Soil Moisture on Clubroot 551 
based upon observations with no direct experimental work. He frequently 
found a severe attack of the disease associated with heavy rainfall. In 1903 (16) 
he refers to a plot in which turnips were planted just previous to a heavy rain. 
The plants came up w T ell, but had a sickly appearance from the start and were 
uniformly infected even where lime had been applied. In this same plot two 
years later he observed that the disease first appeared after a heavy rain of several 
days* duration and spread rapidly thereafter. In summarizing his observations 
on the influence of different seasonal conditions upon the occurrence of the dis¬ 
ease (13) he was able to find no indication of a uniform severity or absence of the 
disease in any given area over a period of several years. He cites a number 
of cases where the disease was more severe on low ground, although he often 
attributes this to other causes in addition to excessive soil moisture. He reports 
( 14 ) one plot which was planted on low ground where considerable water remained 
from fall to spring, although it was artificially drained. In this plot he observed 
that infection was most severe in the lower portions, which he attributed to 
excessive soil moisture and recent cultivation of turnips on the area. In another 
publication (13) he states that other things being equal, the disease is worst on 
the low parts of the field with wet, cold, and "sour” soil. He quotes 23 eases 
observed in 1905 and 1906, all of which show that the more moist the soil, the 
more malignant the infection. In a survey of plant diseases for 1916 and 1917 
he again reports (17, p. 312) a case on low ground where infection was severe. 
Although this land had never been in cultivation before, only 6 of the 300 plants 
produced heads, all the others being destroyed by clubroot, probably in associa¬ 
tion with maggots. He also found that land which was poorly drained favored 
the development of the disease as did the low areas. 
He refers to one plot (14) which had poor drainage where infection was un¬ 
usually malignant at the close of August and continued to destroy the plants 
until harvest. The almost total destruction of the stand, notwithstanding the 
application of lime in the experiment, he considered as due to several cooperat¬ 
ing circumstances, chief of which were probably deficiency of lime and defective 
drainage for he points out that on adjoining property having the same type of 
soil but which was well drained and marled there was little or no infection. 
Two other plots of this series at times showed severe infection in parts where 
drainage was not adequate, and he thought that this factor was partly respon¬ 
sible for the presence of the disease in this extreme form. He wrote (13) of a 
case where the disease had been increasing in severity for a number of years on 
an area which needed drainage. In 1901 the soil was drained, and the destruc¬ 
tion due to clubroot was considerably reduced and had not increased since then 
in spite of the fact that cultivation of cabbage had been continued. He con¬ 
cluded that the moisture conditions of the soil were so important that all pre¬ 
cautions against the disease are valueless when drainage is not perfect. He thus 
modified his recommendation of lime as a control for clubroot. After the long 
series of observations with Christensen and Harder (4) he recommends for 
control of this disease, a correction of acidity by liming. But where the soil 
does not need lime and the fungus is still present, he suspects defective drainage 
or some unfavorable physical condition of the soil and advises that these conditions 
be improved. He was convinced (16) that on well-drained arable land where 
there is sufficient calcium carbonate the introduction of the clubroot fungus 
will not cause any serious infection. As an explanation of the effect of weather 
conditions on the occurrence of clubroot, he seemed inclined to believe that an 
abundant precipitation at the time when the myxoamoebae swarm in the soil 
will favor infection in a high degree, but he offers no proof of this. Conversely, 
he states that a warm, dry period in later stages of the disease may make it 
worse, since he frequently noticed infected turnip and rape plants wilting in 
