Nov. 15,1925 Temperature for Potato Infection by Fusarium oxysporum 919 
ture in this process, since the time involved was usually less than a 
minute. The 12 tanks were paired, and six different temperatures 
maintained. Comparisons between the temperature of the tank and 
the temperature of the soil in the cans at the depth at which the 
potatoes were showed them to be the same. 
THE PRELIMINARY EXPERIMENT 
The temperatures for the preliminary experiment were 14°, 16°, 
18°, 20°, 22°, and 24° C. Readings were recorded every 2 hours, 
although corrections were frequently made oftener. The first 
experiment ran from 6 p. m. February 16, 1922, to 6 p. m. February 
26, 1922, a period of 240 hours. An effort was made to maintain 
the greenhouse temperature at about 18° C., but it rose during the 
day and frequently fell during the night. Even with care there 
were deviations from the desired temperatures, but rarely more 
than two or three tenths of a degree. The tank at the high-tem- 
perature end of the bin came too near the heating pipes, and the 
temperature was kept down with difficulty. 
The average deviation for the period of the experiment is given 
in Table I. 
Table I. —The temperature which it was desired to maintain in each tank in the 
preliminary experiment, together with the average deviation for the experimental 
period, expressed in degrees centigrade 
Desired temperature.... 
Average deviation: 
First tank.... 
14.0 
16.0 
18.0 
20.0 
\ 
22.0 
24.0 
+0.049 
+0.013 
-0. 002 
-0.003 
-0.020 
-0.010 
Second tank.... 
+0.005 
-0.049 
+0.002 
+0.052 
+0.027 
+0.142 
At the termination of the experiment the cans were opened and 
the seed pieces examined for evidence of infection. The seed pieces 
in the control cans were clean, the cut surface bright. To all appear¬ 
ances they were about as when planted. The seed pieces inoculated 
with Fusarium oxysporum showed varying degrees of infection, and 
all of them showed evidence of contact with the fungus. At 24° C. all 
were well infected, the decay varying in depth from 2 millimeters to 
1.5 centimeters, the epidermis was shrunken, and the flesh discolored. 
At 22° all were well infected, though the infection was not as far 
advanced as at 24°. At 20° and 18° all pieces were infected in much 
the same manner as at 22°, but with less penetration into the flesh 
of the seed piece. At 16° infection was more moderate, all pieces 
were infected, but decay penetrated only to a depth of about 2 
millimeters. At 14° infection was not apparent. The inoculated 
surface was dark, the tissue was slightly browned just under the 
surface, and there was no shrinking at the edges. Upon reisolating 
the fungus it was secured in pure culture from all of the seed pieces 
maintained at 16° or higher, and from two seed pieces held at 14°. 
FINAL DETERMINATION OF CRITICAL* TEMPERATURE FOR 
INFECTION 
In order to more carefully determine the temperature at which 
infection occurs the experiment was repeated, a restricted range of 
temperatures being used. The cans were sterilized, the soil was pre- 
