2 BULLETIN 1029, U. S. DEPARTMENT OE AGRICULTURE. 
source of primary inoculum the following year. As he pointed out, 
it has been the experience of many growers that the appearance of 
this disease in epiphytotic form in a given locality is usually asso- 
ciated with a certain lot of cabbage seed. Observations by the writer 
have strengthened the belief that infected seed is the chief cause of 
heavy losses from black-leg. 
Henderson (S) found that naked pycnospores of Phoma Ungam 
were killed within two or three minutes by 1 : 200 formaldehyde or 
1 : 1,000 mercuric-chlorid solutions. Spores within pycnidia em- 
bedded in soft cortical tissues of the host were killed after 21 minutes 
by the formaldehyde solution, while with the other fungicide a few 
spores were still viable after this length of treatment. Henderson's 
study was limited by the small number of infected seeds available. 
It was found, however, that after treatment in 1 : 200 formaldehyde 
solution for 21 minutes or in 1 : 1,000 mercuric-chlorid solution for 
10 minutes, infected seeds still yielded pure cultures of Phoma 
Ungam. 
In 1917 a crop of the yellows-resistant Wisconsin Hollander seed 
was grown at Racine, Wis. A scattering of Phoma Ungam developed 
on the seed plants, and a very small percentage of the pods became 
infected. All of this seed (approximately 25 pounds) was treated 
with a 1 : 256 solution of formaldehyde, and most of it was planted 
in the same locality the following season. Black-leg developed in 
epiphytotic form in most of the seed beds, resulting in heavy crop 
losses where such plants were set in the field. A typical field from 
this lot of seed as it appeared at the end of the season is shown in 
Plate I, A. The uniformity with which the disease developed in beds 
from the lot of seed in question and the fact that many of these beds 
were on soil which had not grown cabbage for many years left no 
doubt that the fungus carried over in the seed was the source of in- 
fection. Moreover, it was evident that despite seed treatment the 
parasite had spread from comparatively few centers to a large per- 
centage of the plants during their growth in the seed bed. 
This situation raised the inrportant question as to how much re- 
liance is to be placed upon seed treatment as a means of control for 
black-leg. Experiments and observations reported later in this paper 
show that a very small percentage of infected seeds may under cer- 
tain environmental conditions cause almost a total loss of the crop. 
Moreover, the detection of such infected seeds is very difficult, even 
by an expert. Since a very large portion of the cabbage seed used 
in this country is grown in a few restricted areas in America and 
abroad, the average grower uses seed concerning the history of which 
he knows very little, and this fact makes it the more necessary either 
that seed treatment be entirely effective or that the production of 
Phoma-free seed be insured. 
