8o 
Journal of Agricultural Research 
mvin. No. 3 
consideration, for it was characterized by a decay of the stem beginning 
at the base and extending upwards. 
It is to Smith (31) that we owe pur first tnorough study and careful 
description of a bacterial disease of the potato stem and tuber. How¬ 
ever, the disease, caused by Bacillus solanacearum Smith, belongs to a 
distinctly different type than blackleg. 
As far as the writer has been able to discover, Frank, in Germany, 
(13, 14) appears to be the first writer definitely to connect the blackleg 
disease or “Schwarzbeinigkeit” of the potato stem and the accompanying 
wetrot of the tuber with a bacterial parasite. It is evident that the dis¬ 
ease had been known and recognized there for some time, but it had 
been associated with various fungi. Frank’s description of Schwarz - 
beinigkeii is definite and clear, and it agrees very closely with certain, 
but not all, of the characters of the blackleg as observed by the writer 
in Maine, Vermont, New York, and in some of the* Middle West and 
Rocky Mountain States. 
The organism, to which the specific name “ Micrococcus phytophthorus” 
was applied in the second paper, was found to be constantly associated 
with the disease and capable of producing it when inoculated into 
healthy stems. It is interesting to note that all other organisms described 
as causing a similar type of disease are bacilli and are of greater length 
than the diameter, 0.5/i, which Frank gave for the cocci he described. 
In this connection, however, it may be mentioned also that Frank 
stated that for four years, material studied by him from different regions 
invariably showed organisms of the type he described. 
In 1901 Delacroix (9, 11) described what appears to be still another 
type of bacterial disease of the potato stem for which was suggested the 
name “brunissure” or browning. He gave the name “ Bacillus solan - 
icola” to the causal organism. As in the case of blackleg, the first visible 
signs of disease are a yellowing of the foliage and cessation of growth, fol¬ 
lowed by the gradual death and drying up of the plant. The stems die 
from the base upward, but are described as browned rather than black¬ 
ened; and cross sections show transparent brown patches, which may 
extend some distance up the stem. A prominent characteristic is the 
development of a gummy material and tyloses in the wood vessels of the 
stems of attacked plants. 
It is evident that this disease, like that caused by Bacillus solanace¬ 
arum, is of a type entirely distinct from blackleg and therefore need not 
be considered further, especially since cultures of the organism are no 
longer available for comparison. It may be mentioned, however, that 
Delacroix considers it to be a soil organism, and the chief source of 
infection is from the soil by means of wounds. Tubers are also attacked, 
the disease entering from the stem end and causing a browning of the 
tissues. 
