374 BULLETIN No. 189 [June, 



hence we may conclude that this fungus was very abundant both in the 

 soil and on the plant parts in contact with the soil. 



Survey of Plot Used for Field Inoculation Experiments, May 6 

 to May 11, 1914. -This plot, formerly used by the Agronomy Depart- 

 ment, had been under cultivation for a number of years. The pre- 

 vious season the field had been in potatoes and corn. The old potato 

 stalks were left scattered over the field during the winter. 



A survey of the plot was made before plowing, following the same 

 method as was used as in the preceding experiment. Sixteen flats 

 were set out twenty-five feet apart. After five days an examination for 

 the presence of Rhizoctonia was made. By microscopic examination 

 and pure cultures, Rhizoctonia was detected in ten trials out of sixteen 

 on this plot. 



Survey of Agronomy Plots on Xortli Farm, September 26 to Octo- 

 ber 2, 1914. Here a more extensive survey was conducted. The 

 agronomy plots on the North Farm were chosen for this purpose be- 

 cause of the fact that they had been under continuous cultivation 

 since 1895, and showed the effects of different methods of soil treat- 

 ment, various systems of crop rotation, and the application of differ- 

 ent kinds of food. (For treatments and rotations used, see Fig. 24.) 

 These plots are also typical of the prairie soil, which represents the 

 most extensive and important type of soil in Illinois. 



The procedure followed in this survey was modified as follows: 

 Instead of a flat, a seven-inch flower pot, which could be easily steri- 

 lized and dried, was employed. Small cheesecloth bags were filled with 

 sphagnum moss; these were sterilized in the autoclave. When ready 

 for use, the bags were moistened and placed in the bottom of the pots 

 and secured in such a way that they remained in position when the 

 pots were inverted. A small patch of soil, one in each plat, was lev- 

 eled off, only a small living plant or some plant debris being left. 

 Several thicknesses of moistened filter paper were then laid over the 

 spot, and a flower pot was placed over the whole. The pot was pushed 

 into the ground about three inches and the soil heaped up around it 

 on the outside. The pots were left in this condition about one week, 

 during which time the moss was moistened at intervals. Conditions 

 were very favorable to the growth of Rhizoctonia if it was present 

 in the soil. When the pots were lifted, the plant parts or debris with 

 some of the soil were wrapped in the filter paper and placed under 

 bell jars. The contents of the papers were then examined for the 

 presence of Rhizoctonia. 



These plots showing the effects of diverse treatments yielded R. 

 Solani in sixty-four trials out of seventy. The six negative results 

 were scattered over the field, so that no correlation between the treat- 

 ment of the plot and the presence of Rhizoctonia can be said to exist. 



