372 BULLETIN No. 189 [June, 



ample, while the average length of a cell from " Cotton I" was only 

 65/t, the largest reading was 127. 5/x, which was higher than the small- 

 est measurement of a cell of the strain ' ' Chenopodium, ' ' whose aver- 

 age reading was 110/x higher than that of "Cotton I." If measure- 

 ments are made of hyphae forty-eight hours old, the differences are still 

 more striking, even in the same strain. 



Hence, on the measurement of mycelial cells of RMzoctonia Solani, 

 as on the study of the growth on media, no conclusions can be based in 

 regard to distinguishing the strain* of this difficult species. 



SOIL SURVEY OF RHIZOCTONIA 



As shown in Table 1, RMzoctonia Solani has been observed in al- 

 most every state in the Union, and causes injury to a large number of 

 plants under various conditions and in widely different types of soils. 

 To determine to how great an extent Rhizoctonia is actually present 

 in the soil, several surveys were made at the University of Illinois in 

 fields containing a variety of plants. 



Survey of the Perennial Garden, Horticultural Grounds, April 28 

 to May 1, 1914. During the summer and fall of 1913, Rhizoctonia 

 was isolated from a number of perennial plants in the garden. To 

 determine whether the fungus lived on the dead parts of the plants 

 or in the soil or both during the winter season, a survey was made the 

 following spring. 



Since it is somewhat difficult to isolate Rhizoctonia directly from 

 the soil by means of soil cultures, the following method was devised 

 to determine its presence in the soil : Small patches of ground were 

 selected over the field about twenty feet apart, so that the results might 

 give a fair idea of the distribution of the fungus. Each space was 

 cleared except for a small living plant, and the soil thoroly watered. 

 Three sheets of moistened filter paper were then placed on the 

 ground over the plant. To prevent evaporation, a small flat with a 

 layer of wet moss attached to the bottom was placed over the paper. 

 The flats had previously been sterilized in formalin (1-100) and the 

 moss sterilized in the autoclave. Thru several small holes in the bot- 

 tom of the flat, water was added to the moss from day to day to keep 

 it moist. At the end of the fifth day the plant parts were removed 

 to the laboratory. 



The presence of the fungus was determined by means of pure cul- 

 tures and by microscopic observation. Where the identification de- 

 pended solely on microscopic observations, the material was left in a 

 covered dish for several days until the strands of the fungus became 

 older, when they could be distinguished more readily by their color. 



In thirteen cases out of sixteen Rhizoctonia was found present on 

 the dead or living pieces of plants placed in contact with the soil ; 



