New YorK AGRICULTURAL EXPERIMENT STATION. 63 
parchment, the blackened veinlets standing out sharply against 
the brown background. As the leaves in the head become affected 
they decay, producing a dark, vile-smelling mass. 
This trouble was brought to the attention of pathologists at 
the time of an epidemic when the loss in infected fields was 
often total and consequently an exaggerated idea of the average 
fatality of the disease arose. Study extended over a number of 
seasons has shown that the true epidemic aspect appears only 
under unusual combinations of several factors, prominent among 
which are high temperature and abundant moisture. Under usual 
conditions a majority of the plants in a field may be infected and 
yet mature a considerable crop although a smaller one than 
would have been otherwise produced. In the latter case the dis- 
ease.may pass unnoticed except by those familiar with its appear- 
ance. 
The black rot of cabbage is caused by Pseudomonas campestris 
(Pam.) Smith, a species of bacterium which attacks several spe- 
cies of the Crucifere. This germ is widespread in the United 
States east of the Mississippi river; and in September, 1902, Prof. 
W. Paddock sent us a diseased cabbage from Colorado affected 
with what he believed to be black rot. In a letter accompanying 
the specimens he stated that this disease had been destructive in 
Colorado in 1901 and 1902. We established the correctness of his 
diagnosis by isolating P. campestris and determining its patho- 
genicity upon young cabbages in the greenhouse. While the pres- 
ence of P. campestris in Europe? was not reported until 1899, the 
promptness with which this report has been confirmed by observers 
in England,’? Holland,t Denmark,’ Austria® and Switzerland’ sug- 
gests that it is there widespread and of long standing. 
*Harding, H. A. Die schwarze Fiulnis des Kohls und verwandter Pflanzen, 
eine in Europa weit verbreitete bakterielle Pflaiizenkrankheit. Cent. 7. Bakt., 
etc., II. Abt., 6: 305-313. 1900. 
3Potter, M. C. On the Brown Rot of the Swedish Turnip. Jour. Board of 
Agr., 10: 314. 1903. 
4van Hall, C. J. J. Twee Bacteriénziekten. Tijdsch. over Plantenziekten, 6: 
169-177. 1900. 
®Rostrup, E. 17. Oversight over Landbrugsplanternes Sygdomme i 1900. 
Sep-Abr aus Tidsskrift for Landbrugets Planteavl, 8: 109-128. Kjébenhavn, 
1901. (Ref. Zeit. 7. Pflanzenkr., 12: 293. 1902.] 
‘Hecke, Ludwig. Eine Bakteriose des Kohlrabi. Zeitschrift fiir das land- 
wirthschajtliche Versuchswesen in Oesterreich, 1901. 8.469. ~[Ref. Zeit. f. Pflan- 
zenkr., 11: 273. 1901. 
7Brenner, W. Die Schwarzfiiule des Kohls. Cent. f. Bakt., ete., 1. Abt., 12: 
275-735. 1904. 
