70 
Journal of Agricultural Research 
Vol. XXrV» No. t 
Examination of the Tables V-VII shows considerable variation in 
susceptibility as between individuals at all temperatures. This varia¬ 
tion is manifest not only by length of incubation period but also by 
extent of infection and rate of development of the disease once infection 
has occurred. At and above 26° C. the incubation period is materially 
shortened for a great number of individual plants, especially those of 
the Wisconsin Hollander strain. In naturally infested soil Wisconsin 
Hollander plants which escape the disease for the first 20 days usually 
remain healthy, even though they are growing at high temperature. In 
artificially inoculated soil all of the plants become diseased within the 
first 20 days as a rule. 
Plants of the Wisconsin Hollander strain which showed symptoms of 
yellows even when very young have been observed to overcome the attack 
and resume vigorous growth. Their ability to do this was less pro¬ 
nounced in plants grown in artificially inoculated soil. It will be seen 
from Table VII that a high percentage of plants were killed in the arti¬ 
ficially inoculated soil. The sudden death of some plants, the ability of 
others to overcome the attack, and the ability of still others to escape 
the disease entirely, furnish evidence of a variation in degree of resistance 
of the individual plants during the early stage of development. The 
same condition has been known for several years to exist among .varieties. 
However, still more significant is the fact that such variations in degree 
of resistance continue to appear as between individuals of the most 
resistant and most stabilized of the Wisconsin strains. 
Our main interest lies, therefore, in the variations in resistance as 
between individual plants. The facts cited as bearing on this variation 
indicate that Fusarium resistance in cabbage is due to hereditary factors, 
probably multiple, and that many of the plants are entirely lacking in 
one or more of the factors for resistance or possess them in a hetero¬ 
zygous condition. The Wisconsin Hollander strain was selected to resist 
the Fusarium disease under certain conditions to which the plants are 
normally subjected in the field. Plants which resist under these condi¬ 
tions may not possess sufficient factors for resistance to enable them 
to resist under more severe conditions, as evidenced during very hot 
summers. Because of the fact that the seed plants are grown under 
conditions which permit free intercrossing, the tendency is for them to 
remain in this heterozygous condition even when grown in “sick'' soil. 
When the seed plants are grown on ‘‘sick soil, however, the plants which 
possess an insufficient number of factors for resistance develop the dis¬ 
ease and are discarded. Thus, by selecting seed plants from “sick'' 
soil, it is possible to maintain a resistant strain, under the conditions 
selected, even though it may not be homozygous for resistance. 
R^I/ATION OF AGH OF SE:eDIvINGS TO EXPRESSION OF THE RESISTANT 
CHARACTER 
It has been shown (Table V) that during the first 20 days of develop¬ 
ment the Wisconsin Hollander plants are practically as susceptible to 
yellows at the higher temperatures as the susceptible commercial strain. 
On the other hand, the Wisconsin Hollander strain shows a high degree 
of resistance by the time the plants are old enough to be transplanted 
into the field. Since this condition has manifested itself for several sea¬ 
sons and since the plants are usually grown in soil with a fairly low tern- 
