444 
Journal of Agricultural Research 
Yo\ XXIV, No. 6 
HUMIDITY 
A high relative humidity (about 95 per cent), maintained by means 
of distilled water in evaporation pans, was used throughout these experi¬ 
ments. The uniformity of the humidity throughout the chambers was 
maintained by the circulation of the air by means of a fan. In the 
absence of air circulation there would be, undoubtedly, a higher relative 
humidity in some parts of the chambers than in others, depending on 
the vapor pressure in the particular area. 
GASES 
In order to eliminate any possible. effects of gases given off by the 
sweet potato or other vegetables, provision was made for a constant 
exchange of air, to be drawn through the chambers slowly by means of 
a vacuum pump. The amount of air drawn out was roughly deter¬ 
mined by drawing it through wash bottles and regulated by stop-cocks. 
materials 
The Little Stem Jersey variety of sweet potatoes grown and stored 
at the Government experimental farm at Arlington, Va., was employed 
in these experiments. The potatoes were cured for a period of 10 days 
at temperatures from 25° to 30° C., and held as nearly as possible 
throughout the season at temperatures between 10° and 14°. 
The following species of Rhizopus were employed: R. nigricans, R, 
tritici, R. oryzce, R. reflexus, and R. artocarpi. They were grown on 
sweet potato agar at a temperature of 20° C. 
EXPERIMENTAL DATA 
Four types of experiments were used. The methods employed, the 
purpose of the experiments, and the data obtained will be discussed in 
connection with each type of experiment. 
TYPE ONE 
In the first type of experiments the potatoes were merely wounded 
and placed in the storage house at the Government experimental farm 
at Arlington, Va., and at different temperatures in the infection cham¬ 
bers. The potatoes were wounded by striking them three or four times 
on the blunt rim of a wire basket, after which they were placed in wire 
baskets 12 inches deep and 12 inches in diameter, which were in turn 
placed in the sweet potato storage house or in the infection chambers. 
The purpose of these experiments was to determine what organisms 
cause decay where infection depends upon the organisms present on the 
potatoes. The scope of the experiments in this connection was limited 
to potatoes grown and stored at Washington, D. C. The number of 
species and the number of spores of each species present on the potatoes 
might be expected to vary with the locality in which the potatoes were 
grown, the conditions under which they were stored, and the conditions 
prevailing in the railway car during transit to the markets and in the 
markets Siemselves. The number of spores of a given species also might 
be expected to vary with the season of the year; in fact, it has been 
shown that there are fewer spores on the potatoes at digging time and 
