THE CONTROL OF CABBAGE BLACK-LEG. 
17 
very small in the protected portion of the plat as compared with that 
in the portion exposed to natural rainfall. 
Table VI. — Effect of variation in rainfall on the development of black-leg on 
cabbages in the seed bed at Madison, ^Yis., in 1920. 
lot. 
No. 2-19 
No. 2-19 
No. 7-19 
No. 7-19 
Treatment. 
Extent of disease at 
the end of the ex- 
periment. 
Number 
of plants 
exam- 
ined. 
Covered during rains 94 
Exposed to natural rainfall 117 
Covered during rains i 135 
Exposed to natural rainfall i 355 
Diseased 
(per cent). 
2.1 
81.1 
4.4 
49.8 
It is, therefore, undoubtedly true that in regions where cabbage 
plants are grown in open seed beds, variation in the rainfall which 
prevails during the period between the appearance of primary pyc- 
nidia and transplanting has a very great influence upon the develop- 
ment of black-leg. This fact should also be of value in checking the 
disease by avoiding the splashing of water where the plants are grown 
in covered coldframes or in greenhouses. 
IMPORTANCE OF SPREAD IN THE SEED BED AS COMPARED WITH DISSEMINATION 
IN THE FIELD. 
The question of the importance of the spread in the seed bed as com- 
pared with that in the field is, of course, to be considered in inter- 
preting the development of the disease in midseason or later. It is 
natural to exjDect that the greatest amount of dissemination of the 
fungus from plant to plant takes place under the crowded condition 
in the seed bed and during the process of pulling and setting plants. 
Henderson {3) found that when plants showing no visible signs of 
the disease were taken from an infected seed bed and set into clean 
soil, a high percentage of them developed typical black-leg lesions on 
stems and roots within a few weeks. An instance is cited later in this 
paper (see fields 1 and 2 in Table IX; also PI. II) where early and 
late planting from the same seed bed resulted in a wide difference in 
the destructiveness of the disease, due to the dissemination of the 
fungus after the first plants were removed. Numerous field observa- 
tions have been made where black-leg wilt affected alternate plants in 
a row, as a result of the fact that one of the two droppers on the 
transplanting machine 3 had set diseased plants. Many cases have 
3 The machine referred to is the transplanter commonly used in many sections for 
setting out cabbage, tobacco, and tomato seedlings. The setting is done by two persons, 
who place the plants alternately in the furrow, coincident with the release of a small 
quantity of water from a supply tank. One row is planted at a time. 
