84 
Journal of Agricultural Research 
Vol. XXIV, No. t 
(i i) It thus appears that the optimum temperature for the vegetative 
growth of the fungus in culture practically coincides with the optimum 
for the development of yellows in seedlings. This is above the optimum 
for the growth of the host plant. 
(12) Cabbage seedlings grew at all temperatures from 14° to 38° C., 
but only very poorly at the latter. At 38° the seedlings emerged from 
the soil, but most of them died before developing any true leaves. The 
optimum soil temperature for seedling growth was found to be about 
20° when the Wisconsin tank method was used. 
(13) Soil temperature greatly influences the length of the incubation 
period for the disease. Under controlled conditions the incubation 
period varied from 18 days at 17° C. to 8 days at 29° to 32°. 
(14) With constant favorable temperature yellows developed at any 
percentage of soil moistiure permitting growth of cabbage seedlings. In 
soil with a moisture-holding capacity of 46 per cent the yellows developed 
more rapidly and destructively in susceptible plants when the moisture 
was held at 15 per cent than at 19, 23, or 26 per cent. At 19 per cent 
moisture the disease appeared two days later than at 15 per cent, but 
once it had started the subsequent rate of development was about the 
same in both cases. 
(15) Nineteen per cent soil moisture was the most favorable for the 
growtJi of cabbage seedlings when the soil temperature was held at 
23® C. and the air at 14° to 18®. The growth of plants was materially 
checked at 26 per cent and also at 15 per cent soil moisture. At these 
less favorable moistures the color of the foliage was quite abnormal. 
Plants grown at 19 per cent soil moisture had healthier color and a more 
extensive root system, and the dry weight was almost twice that at 26 
per cent moisture. Thus it is evident that the soil moisture (15 per cent) 
which was too low for good growth of the host plant was most favorable 
for the development of yellows, while the soil moisture (19 per cent) which 
proved almost equally as stimulating to the disease was highly favorable 
for normal development of the host plant. 
(16) The preceding conclusions relative to the relation of soil temper¬ 
ature and soil moisture to the occurrence of yellows in cabbage seedlings 
were first worked out in the greenhouse under experimentally controlled 
conditions. 
(17) Soil temperature and soil moisture influenced the occurrence of 
yellows in the field in a manner similar to that in the greenhouse. With 
seedlings started in May, June, and September when the soil temperature 
was low, the disease showed a lower percentage and was slower in appear¬ 
ing than with those started in July and August when a high soil tempera¬ 
ture prevailed. 
(18) These facts, no doubt, are of significance in the geographical 
distribution of the disease. In the Southern States, where cabbage is 
generally grown commercially as a winter or early spring crop, the soil 
temperature is very probably too low for the organism to gain a foot¬ 
hold on such plants. Reports from these sections indicate, however, 
that where once introduced the Fusarium establishes itself on summer- 
grown cabbage or other related hosts and may be expected to persist 
and attack the crops whenever soil temperature is favorable. 
(19) The foregoing conclusions are based on the general or average 
behavior of the cabbage seedlings. It is in this connection that note¬ 
worthy variations in the incubation period as between certain individual 
plants in the same receptacle may be as great as between some plants 
