1897] The Bacterial Diseases of Plants: 137 
(15) Effect on Growth of Reaction of Medium (acid, neutral, alka- 
line)—No specific statement. Organism will evidently grow 
in either acid or alkaline media. 
(16) Sensitiveness to Antiseptics and Germicides—No state- 
ment. 
(17) Other Host Plants—No mention of any. 
(18) Effect upon Animals.—No mention of any tests. 
(III) Economic Asprcts: 
(1) Losses.—Serious. 
(2) Natural Methods of Infection —The question at once arises : 
How is the disease spread in the field, the tuber being, as is 
well known, carefully protected from external injuries by a firm 
layer of cork cells. If this layer is not punctured or broken 
the tuber appears to be safe from parasitic attacks. Even when 
the bacillus was placed on the cut surface of a living tuber in 
the air of an ordinary room, Dr. Kramer found that it was 
never able to cause the disease, the tuber developing a protec- 
tive layer of cork cells under the mass of bacilli before they 
could grow. The case was quite different, however, when 
tubers lying in the infected nutrient solutions were stabbed 
with a sterile platinum wire. When, after 8 days, such tubers 
were examined by cutting through the stab, the canal in most 
cases was found occupied by the bacteria, and the decay of the 
tissue was seen to have proceeded from this canal outward. 
If the cork covering was shaved off in any place, the infection 
_ ordinarily began there. There is, consequently, no doubt that 
in the presence of sufficient moisture the bacteria can gain an 
easy entrance if the corky covering of the tubers is injured in 
any way, and such injury, we know, is frequently brought 
about by insects. It is well known also that the lenticels open 
when potato tubers are exposed to moisture for some time, 
e. g., in wet earth, and this readily accounts for the infection of 
uninjured tubérs. Indeed, Dr. Kramer demonstrated experi- 
mentally that in apparently uninjured tubers lying in his in- 
fected‘broths the rot frequently began with a darkening and 
softening around the lenticels, these changes being visible 
Wwithinfa few days. When such spots were examinsd it was 
found that the bacteria had already penetrated into the tissue 
