Jan. is, 1917 
Blackleg Disease of Potato 
121 
In the case of the organism received from Schuster and carried under 
the name of B. phytophthorus , the yellow growth was apparent on both 
agar and potato. Upon the latter the growth was of a very distinct 
lemon yellow, considerably deeper than that produced by the other 
organisms. 
NOMENCLATURE AND RELATIONSHIP 
An analysis of the data obtained as the result of these comparative 
studies seems to point to but one conclusion. When subjected to the 
various differential tests at the same time and under the same condi¬ 
tions, the cultures received under the names “Bacillus atrosepticus Van 
Hall, ” “Bacillus solanisaprus Harrison,” and “ Bacillus melanogenes Pethy- 
bridge and Murphy" and the three strains of organisms isolated from 
potato plants affected with the blackleg disease from widely separated 
parts of Maine appear to be identical. 
It is the writer's opinion that the pathogenic organisms studied should 
be classed as one species, or at the most strains of the same species. The 
only constant differences noted were slight variations in size, shown more 
particularly by B . solanisaprus and IIIA, and the production of a slight 
viscidity on different kinds of media shown by B. solanisaprus and B. 
melanogenes , but not by any of the others. 
It is evident that the two organisms which the writer received and 
studied under the name of Bacillus phytophthorus Appel were not alike, 
nor were they the same as the one originally described by Dr. Appel. 
There is nothing in the data here presented which bears on the rela¬ 
tionship between the organism originally described by Dr. Appel as B . 
phytophthorus and the other strains of blackleg bacteria. As has already 
been stated, Dr. Smith states that it and B. solanisaprus are not iden¬ 
tical, but are closely related. While the writer regrets that he was 
unable to get an authentic, virulent culture of this organism for compari¬ 
son in time to make use of it he has no reason for questioning this state¬ 
ment, coming from so good an authority. 
While the present studies are primarily concerned with relationship, 
the results obtained make it impossible to entirely ignore the question 
of nomenclature. If it is granted that B. phytophthorus differs from B. 
solanisaprus and consequently from the others under consideration, which 
of the three other names should be retained? On grounds of priority, 
B. melanogenes is excluded and the choice is between B. atrosepticus 
and B. solanisaprus. Also on the grounds of priority alone it would 
seem that the accepted name should be B. atrosepticus , but for certain 
reasons the writer was at first inclined to favor B. solanisaprus . These 
reasons are as follows: According to present standards B. atrosepticus was 
not very fully described in the beginning. Moreover, the culture used by 
the writer was obtained from Krai's laboratory with no statement regard¬ 
ing its origin or authenticity. Also its pathogenicity was erratic or weak, 
67906°—17 - 5 
