484 
Journal of Agricultural Research 
Vol. XXIII, No. 6 
are usually distinctly brown in color, sometimes brownish white, fre¬ 
quently with a dark center giving a “ birds-eye ” appearance. Concentric 
rings, usually are not present, though apparently they may occur (PI. 
1, A, B). 
An interesting symptom frequently evident in the greenhouse after 
artificial infection is the formation of a secondary ring of small lesions 2 
or 3 mm. beyond the circumference of the primary lesion. This ring, 
often perfect in shape, seems to follow as a result of renewed activity by 
the parasite about the primary lesion following a checking of the disease. 
The chlorotic area surrounding the center of infection has been found 
to be relatively free of organisms, as was found by Miss Elliott ( 2 ) in the 
halo-blight of oats. 
PREVALENCE OF THE DISEASE 
The causal organism of the Wisconsin leafspot disease was first isolated 
in the spring of 1917. On account of the similarity of other leafspots, 
nothing conclusive can be said as to the prevalence of the disease prior 
to that time, although the writer feels confident that within 20 years of 
casual observation previous to 1917 he has seen a number of more serious 
cases of the disease than have been noted since. This belief is strengthened 
by the testimony of a number of the older tobacco growers in the State, 
who recall complete losses of portions of crops from “rust,” which, from 
our subsequent observations on nonparasitic leafspots, are not believed 
to develop to such an extent on the type of tobacco grown in this State, 
with the possible exception of the “rust” following mosaic. “Rust” 
following as a result of mosaic is not, however, ordinarily limited to such 
an extent by the topography of the land and the opportunity for infection 
as is the bacterial leafspot. Since 1917 a number of mild occurrences 
of the disease have been seen within a 25-mile radius of Madison, and in 
most cases have been identified by isolation of the causal organism and 
inoculation experiments. Search has been made for this disease in a num¬ 
ber of other tobacco districts, mostly in Kentucky, Maryland, Pennsyl¬ 
vania, and in the Connecticut Valley. Only one specimen has been 
collected which can with certainty be said to be the same disease, and this 
was from Kentucky in 1919. One collection from Connecticut in July, 
1919, proved to be the “wildfire” disease, and was the first record of 
that disease in the Connecticut Valley. Similarly, collections made in 
1920 from Maryland, Kentucky, and Ohio proved to be wildfire. 
ISOLATIONS 
The first isolation of the Wisconsin leafspot organism was made in 
June, 1917, from the seed beds at the experiment station at Madison. 
At about the same time specimens of a leafspot on tobacco seedlings (wild¬ 
fire) were received from Mr. E. G. Moss, in charge of the branch tobacco 
station, Oxford, N. C. This disease was at first thought to be due to a 
fungus, and preliminary isolation and infection experiments were con¬ 
ducted from this standpoint with negative results. Bacteria were soon 
after isolated and infection secured. Word was then received that Dr. 
Frederick A. Wolf, of the North Carolina Station who was working on 
the same disease, had established the bacterial relationship, no doubt a 
few days before our own conclusion had been reached. A few weeks 
later the writer visited the North Carolina section and had the oppor¬ 
tunity of noting a second serious outbreak of the disease in that section. 
