Potato Failures. 
13 
eight rotten tubers, making 40 cultures in all, produced pure cul¬ 
tures of Rhizoctonia in every instance. 
SPREAD OF THE DISEASE. 
Conditions have a marked influence on the development of 
this fungus. The soil and seed may be thoroughly infected and 
still the plants escape serious injury; on the other hand, mere 
traces of the disease under favorable conditions may develop and 
cause serious loss. 
Rate of Growth at Different Temperatures. —Experiments 
show that pure cultures of this fungus on potato plugs and agar 
make very little or no growth in seven days, when kept at a tem¬ 
perature of about 40 ° F.; a slight growth at 55 ° F.; and a profuse 
growth at 72 ° F. 
The Soil. —Some fields seem to be more favorable to the 
development of this fungus than others. A heavy, poorly drained 
soil seems to be most favorable for its development. Potatoes 
grown on heavy soils with good bottom drainage usually suffer less 
severely from this disease than those grown on poorly drained 
land. 
It is not known how long this fungus will remain in the field 
when it once becomes thoroughly established, but observations of 
investigators show that it may live indefinitely on dead organic 
matter in the soil and on the roots and stems of various plants. 
Influences of Heat and Moisture .—It has frequently been 
noticed that the corticium stage of the fungus develops freely on 
the surface of the ground under the potato plants and on the stems 
of the green plants when the ground is kept too wet during a spell 
of hot weather. This stage is of a light gray color and might 
easily be mistaken for alkali. However, some growers are quite 
familiar with it and know too well that its appearance on the 
ground under the plants indicates an over supply of water 
and a lack of air circulation at the base of the plants, and are well 
aware that if conditions are not improved the plants will be 
severely injured. 
Laboratory work shows that a high temperature and plenty 
of moisture are necessary for the rapid development of this fungus. 
This possibly explains why extremely hot weather occasionally 
severely injures the plants in fields which have been thoroughly 
watered, while those in fields which have been sparingly watered 
and well cultivated remained apparently uninjured. In our ex¬ 
periments, when diseased plants were kept comparatively dry and 
well cultivated they did fairly well, but when such plants were over 
watered and the ground became too wet and soggy, the subterranean 
