458 Wisconsin Academy of Sciences, Arts, and Let Vers. 
Explanation of Plates 
plate XXXIXI 
Tomato plants and cultures of the tomato-wilt fungus, showing the 
effect of different temperatures. (Photographs by E. E. Clayton.) 
Pig. 1. Normal tomato plants grown in sterile soil at temperatures of 
19°, 22°, 24°, 28°, 31°, 33°, and 35° iC. This shows the effect of these 
various temperatures on the development of the tomato plant, the op¬ 
timum being at about 28°-31°. 
Pig. 2, Tomato plants grown at temperatures of 19°, 22°, 24°, 28°, 
31°, 33°, and 35° C., in soil infested with the tomato-wilt fungus. Note 
that the plants escape the disease at the two extremes, whereas the wilt 
appears first and develops most severely at 28°-31°. 
Pig. 3. Petri dish cultures of the tomato-wilt fungus showing growth 
at temperatures of 8°-38° C. The maximum temperature for the develop¬ 
ment of the fungus is between 35° and 3'8°, the optimum about 28°, and 
the minimum between 8° and 10°. Note the close correlation between 
relative vigor of growth of the fungus at these temperatures and the 
development of the disease as shown in figure 2. 
PLATE XXXIV 
The Rhizoctonia disease of potato as shown on the tuber, on the 
young stems, and in the field. (Photographs by B. »L. Richards.) 
Fig. 1. “Black scurf’ on the potato tuber, this being the dormant stage 
of Rhizoctonia. The fungus produces numerous black sclerotia on the 
tuber, which are usually strictly superficial and epiphytic. If such a 
tuber is planted under certain environmental conditions, the fungus de¬ 
velops as a serious parasite on the young shoots. (See figure 2.) 
Pig. 2. Rhizoctonia injury, or “stem canker,” as it appears on the 
young potato sprouts. It kills many of these before they can reach the 
surface of the soil and weakens those which survive. (See figure 3.) As 
explained in the text, the degree of this injury is largely conditional on 
soil temperature. (Compare with Plate XXXY.) 
Fig. 3. Experimental potato field, showing the seriousness of Rhizoc¬ 
tonia damage. The weak plants, row A, grew from untreated, scurfy seed 
tubers. Note that many hills are missing. The strong rows on either 
side (B, etc.) grew from treated seed tubers, the treatment practically 
eliminating Rhizoctonia injury. 
