16 
BTTLLETIX 1029, U. S. DEPARTMENT OF AGEICULTTJEE. 
rain was eliminated the spread of the disease was completely checked, 
while it was enhanced where artificial sprinkling was done. Al- 
though plat 3 was exposed to numerous heavy dews, these were ap- 
parently insufficient for the dissemination of spores for any appre- 
ciable distance. 
Table V. — Effect of variation in rainfall on the development of black-leg on cab- 
bages in the seed bed at Madison, Wis., in 1019. 
Exposed to natural rainfall j 425 
Artificially sprinkled \ 174 
Covered during rains 359 
Covered every evening and during rains 369 
This experiment was repeated in 1920. Two lots of seed, one 
heavily infected (Xo. 2-19) and one mildly infected (Xo. 7-19), were 
planted in clean soil on May 12. Part of the plat was protected from 
rains during the growth of the plants, water being supplied arti- 
ficially, with care to avoid splashing. After the first appearance of 
the disease on May 22, primary infections continued to develop on 
the cotyledons and at the base of the hypocotyl with about equal 
rapidity in the protected and unprotected portions of the plat. Pyc- 
nidia in these lesions were first noted on May 25. By June 11 prac- 
tically all the primarily infected plants were dead, and each bore 
many mature pyenidia. The first secondary infections were noted on 
June 17, and from that time on the disease developed rapidly on leaves 
and stems of the plants in the unprotected portion of the plat. In an 
adjoining plat healthy plants were sprayed with a suspension of 
spores taken directly from lesions on infected plants. The disease 
appeared on these plants about 15 days later. It is thus to be expected 
that even under favorable conditions for dissemination and infection 
the appearance of secondary lesions would not ordinarily take place 
until two or three weeks after pyenidia appeared on plants infected 
from the seed. The plants in the plat were large enough for trans- 
planting by the end of June, when they were pulled and examined for 
the presence of the disease. The results are given in Table VI. In 
spite of the fact that primary infections were very numerous in the 
case of the No. 2-19 seed very little spread to the aerial portions of 
surrounding plants occurred where the splashing of rain was avoided. 
Likewise, with the Xo. 7-19 seed the extent of the dissemination was 
