442 
Journal of Agricultural Research 
Vol. XXV, No. IX 
the host falls completely outside of the dangerous pathogenic range of 
the parasite, and at such a high point as would allow the bean plants at 
their most favorable temperatures to escape practically uninjured. 
Jones' work (Table I, fig. i) indicates that this same temperature 
relation holds equally true for the cotton plant. This agrees also with 
the field observations of Balls (2). 
TEMPERATURE STUDIES WITH THE FUNGUS 
Temperature requirements for the growth of Corticium vagum in pure 
culture have been determined with considerable definiteness by various 
workers. Rolfs (15) found 75 0 F. (24 0 C.) to be the most favorable for 
growth of the fungus. Hartman 11 obtained “no growth at 2 0 , slight 
growth at 8°, fair growth at 13 0 to 18 0 , profuse growth at 24 0 to 25°, 
fair growth at 30°, and no growth at 37 0 C.” The fungus is shown by 
him to have a growth range of from 4 0 to 32 0 with an optimum at 24 0 to 
25 0 . Balls (3) gives 5 0 to 32 0 as the growth range for the fungus and 
23 0 as an optimum for continued growth. At 32°, he states, the fungus 
grows rapidly for two hours and then suddenly stops growth altogether. 
Balls (j) further reports a thermal death point of 50° for the young 
sclerotial cells when exposed at this temperature for a period of two 
minutes. He shows also that the optimum temperature for the growth 
of the fungus is a variable factor, definitely dependent upon the phy¬ 
siological history of the fungus as well as upon the immediate conditions 
under which the fungus is growing. 
The wide temperature range through which Corticium vagum was 
found to destroy living plant tissue made it desirable to determine more 
accurately the temperature limits of the vital activities of the fungus, 
and to discover if possible its optimum temperature requirements for 
growth under varying conditions in pure culture. This latter relation is 
especially desired in view of the the low optimum of 18 0 C. found by 
the writer for the pathogenic activities of the parasite on the various 
hosts. The pressure of other duties, up to the present, has limited the 
work to the ordinary petri-dish method of study which, owing to the 
rapid growth of the mycelium, so shortens the period of observation as 
to lessen seriously the value of the results in interpreting the temperature 
reactions of the fungus. The data so far obtained, however, are of 
sufficient importance in their relation to the general problem to justify 
including them at this point. 
In these studies small squares of a rapidly growing culture of the fungus, 
grown at 25 0 C., were placed in the center of the medium in each of the 
desired number of petri dishes. All the plates were then wrapped in 
sterile paper and kept at exactly the same temperature for 12 hours. At 
the end of this time the colonies were measured and the cultures placed 
directly in the incubators, which were held at the desired temperatures. 
Observations and measurements were made at regular intervals of 24 
hours until the fungus had overgrown the media in the petri dishes. 
This, at the most favorable temperatures, occurred in about four days 
from the time that the temperatures were adjusted. Three series of the 
triplicate cultures were run at different temperatures. The average rates 
of growth obtained in series 1 and 2 are given in Table VIII and are shown 
graphically in figure 6. 
11 Hartman, R. E. a potato disease caused by rhizoctonia. A thesis submitted for the desrree of 
master of science. Unpublished, typewritten copy on file in the University of Wisconsin library. 1915-16. 
