THE CONTROL, OF CABBAGE BLACK-LEG. 23 
Appleton) and at New London (near Shiocton) with those taken at 
Racine shows that the rainy periods from May 15 to June 15 were 
more numerous and as a rule of longer duration in the first two 
localities. It may be inferred from this that there was more oppor- 
tunity for pycnospore dissemination and subsequent infection at 
Appleton and Shiocton than at Racine. In view of the evidence 
already presented as to the importance of rainfall in this connection, 
it is not improbable that this factor was the critical one in deter- 
mining the difference in development of the disease in the three 
localities mentioned. 
These field trials justify the conclusion, as did those made in the 
laborator} r , that neither formaldehyde nor mercuric-chlorid treatment 
of cabbage seed, even if carried to the point where seed injury occurs, 
is a sure preventive of black-leg. Such seed treatment does, however, 
greatly reduce the development of primary infection. This result, if 
coupled with favorably dry weather during the seed-bed period, may 
suffice to give practical disease control, but with more abundant rains 
during this period the disease may develop to a serious extent. It 
should be recalled in this connection that seed treatment with corro- 
sive sublimate is also a successful preventive of seed-borne black-rot 
organisms (12). Since cabbage-seed treatment is a useful precaution 
in these two possible directions and is so simple and inexpensive, it 
is strongly recommended. In the light of our present knowledge, 
soaking in a 1 : 1,000 mercuric-chlorid solution for 30 minutes fol- 
lowed by rinsing in clean water is safest for general use. 
IMPORTANCE OF DISEASE-FREE SEEDS. 
The fact has been brought out that in spite of any practicable seed 
treatment abundant rainfall may cause sufficient spread of the black- 
leg fungus from the few primary infections appearing in the seed 
bed to produce an epiphytotic. Since, therefore, in practice one can 
not rely with confidence upon cabbage-seed treatment for the sure 
elimination of the black-leg organism from infected seed, it is obvi- 
ously important to give increased attention to the securing of seed 
free from Phoma infection. Experience in Wisconsin has shown 
that to accomplish this the crop must be kept clean from the outset ; 
in other words, disease-free "mother seed" must be used on clean 
soil. A large percentage of American cabbage seed is now grown in 
two sections, eastern Long Island, N. Y., and in the Puget Sound 
region of western Washington. In the latter section " mother seed " 
is usually obtained from another locality, most commonly from Long 
Island, Denmark, or England. In the Long Island section local or 
foreign grown " mother seed " is used. In either case the danger of 
introducing black-leg into the seed crop through infected seed is very 
great, since practically none of the growers practice seed treatment. 
