130 The American Naturalist. (February, 
duced into the nutrient solution, and these bacteria. 
had been previously cultivated pure from wet rotten 
potatoes. 
Conclusion.—Pathogenic nature clearly established. 
Remark.—‘ The objection may perhaps be raised that the 
artificially induced wet rot, just described, did not begin with 
infection from without, i. e. from the nutrient solution, but that. 
bacteria were present in the apparently sound tissue of the 
potatoes used for the experiment, i. e. foci of infection dating 
from the harvest time, which later on with higher temperature 
and sufficient moisture, developed further. In opposition to 
this it may be stated, first, that the potatoes used in the experi- 
ment came from a locality in which, in previous years, wet rot 
had not appeared; and, second that the tissue of several of 
these potatoes was tested for the presence of bacteria, but always 
with negative results. The infection was also transmitted to 
sound tubers by puncturing them with a sterile platinum wire 
and then inserting into the stab a slight quantity of a bacter- 
ial, pure culture. These tubers were kept in a damp chamber 
at 35°C. The decay of the tuber, which always proceeded 
from the inoculation puncture, was identical with that of the 
wet rotten tubers. The wet rot of the potato tuber is, there- 
fore, nothing but a decomposition of the same induced by a 
particular species of bacteria. Sorauer, and van Tieghem per- 
formed similar experiments but these differ from my own in 
that the investigators I have mentioned worked neither with 
bacterial pure cultures nor with sterilized tubers and sterilized. 
nutrient fluids.” 
There is another objection which does not seem to have 
occurred to Dr. Kramer, viz., that the tubers which rotted were 
exposed to abnormal conditions. They were either submerged 
or placed in very moist air and quite likely deprived of their 
vitality through lack of aeration. They were also exposed to 
an unusually high temperature. Under these conditions,. 
which would occur in the potato fields only exceptionally 
as the result of exceedingly hot weather and of very frequent 
or very prolonged rains, possibly many other organisms, which 
are usually saprophytic, might enter and destroy the tubers,. 
