148 Dale. — A Bacterial Disease of Potato Leaves. 
except in the doubtful case recorded above, not infrequently showed masses 
of Bacteria, in the condition of zoogloea, inside the tissues of the host and 
between the cells. It therefore seems as if this organism were also patho- 
genic to the potato. 
In the case of plants infected with the original organism, Bacteria 
were sometimes found inside the host plant when no tubes were seen. 
This would seem to be a case of infection without definite tubes like those 
noticed the year before. 
6 . Discussion of Results. 
The experiments and observations recorded above lead to the con- 
clusion that the disease under consideration is bacterial in nature. Various 
bacterial diseases of the potato and allied plants have already been described 
by different authors. A history and comparison of these diseases has lately 
been published by Pethybridge and Murphy 1 in a paper describing a bac- 
terial disease of potato shoots known as ‘ Black stalk-rot ’ or ‘ Blackleg ’, 
occurring in Ireland. 
The bacterial diseases of the potato which have been most fully 
described are the one just referred to, and another worked out by Erwin 
Smith 2 and called by him ‘ Potato Bacteriosis ’, which attacks not only the 
potato but other species of Solanum , especially the egg-plant (S. \Melongena\ 
ovigermn) and tomato ( Lycopersicum esculentum). 
In potato ‘ Black stalk-rot or ‘ Black-leg ’, as described by Massee, 
the symptoms are as follows : 3 The leaves wilt and turn yellow, the 
lowest first. When the leaves droop the surface of the underground parts 
of the stem bearing such leaves is more or less covered with brown stains. 
Discoloration goes up the stem , which becomes black and decays. This 
disease was regarded by Carruthers , 4 who does not, however, describe it in 
detail, to be due to Bacillus phytophthorus , which was first isolated and 
named by Appel . 5 An organism was also isolated by Pethybridge and 
Murphy from potatoes affected with black stalk-rot, but it was not con- 
sidered by them to be the same as (though closely allied to) that obtained 
by Appel. They therefore regard it as a new species, to which they give 
the name B. melanogenes. 
The symptoms of ‘ Black stalk-rot ’ differ considerably from those of 
the disease at present under consideration, especially in the fact that the 
disease begins from below and spreads upwards , attacking chiefly the stems 
1 Pethybridge and Murphy : v. p. 141, supra. 
2 Erwin Smith : A Bacterial Disease of the Tomato, Egg-plant, and Irish Potato ( Bacillus 
solanacearum , n. sp.). U. S. Department of Agriculture, Bull. No. 12, 1896. 
3 Massee : Diseases of Cultivated Plants and Trees, 1910, p. 514. 
4 Carruthers: Journal of the Royal Agricultural Society of England, vol. lxviii, 1907, p. 226. 
6 Appel : see bibliography in the paper by Pethybridge and Murphy quoted above. 
