362 BOTANICAL GAZETTE [NOVEMBER 
and grow well at temperatures considerably above the optimum for 
the first two. It was thought by this selection to obtain more inter- 
esting results than with forms more closely related physiologically. 
Only pure cultures were used. In the test tube cultures from which 
the spores were obtained for use, the fungi were grown upon cylin- 
ders of potato or beet. In either case the liquid ia the tubes was 
a decoction of sugar beets. Other nutrient substances were tried 
for the test tube cultures, but these usually produced modifications 
in the growth of the fungi and it was not found advisable to use 
spores produced on different media in the course of a series of experi- 
ments, the results of which were to be compared. The spores used 
were always taken from cultures that were twelve to sixteen days 
old. The desired temperatures were secured by means of incuba- 
tors and a refrigerator. 
CuarK has pointed out certain sources of error for Van Tieghem 
cell cultures exposed to ordinary temperatures; but the placing of 
cells, made up under ordinary laboratory conditions, at temperatures 
ranging from 5° to 30° C., gave additional opportunity for error. i The 
cells were not entirely closed until they had been left for several minutes 
in the temperature at which they were to remain. This gave opiprs 
tunity for adjustment of air pressure in the cell, but it did not in all 
cases prevent the condensation of water vapor upon the cover glass. 
The small drops of water thus formed not only increased the evapo- 
rating surface but also modified the vapor pressure in the cell. The 
small water drops adjacent to the hanging ones of the nutrient solu- 
tion seemed to sometimes unite with them, thus changing both their 
size and concentration. When the cultures were made in the dry 
air of a furnace heated room no difficulty was experienced, but cells 
made upon sultry days, or when the air of the culture room was 
humid from any cause, gave a visible condensation when placed at 
low temperatures. Even with the greatest precaution this difficulty 
was not entirely overcome. ' 
It was found difficult to examine the cultures placed at besa 
temperatures without interfering with the structure and condition © 
the cells. Examinations were made at temperatures as near as site 
sible to those at which the fungi were growing, and results obtaine 
from damaged cells were rejected. All cultures were observed every 
