The Sterile Fungus Hhizoctonia. 83 



where the fungus is associated with disease, we have as yet no 

 proof that Rhizoctonut is tlie cliief or even partial cause of tlie 

 trouble. It may sometimes be associated with other fungi, perhaps 

 FusariuDi. Atkinson "^ lias indicated that tlie sterile damping off 

 fungus of cotton may perhaps have a part to play in the Fusarium 

 disease of cotton, at least in initiating the disease. 



In spite of the fact that Rhizoctonia is at times an effective 

 parasite, the fungus is probably capable of protracted existence 

 upon decaying organic matter in the soil. In this Avay it may be 

 able to propagate itself, and to spread from plant to plant in the 

 soil even when culture or other means fail to disseminate it. In 

 fact, it seems to be of very general occurrence in the soil, and is 

 likely to be quite commonly found in propagating beds as a cause of 

 damping-off among cuttings and seedlings. From our experience 

 thus far, we venture to predict that few forms of this fungus will be 

 found very selective as to host, and one may well search for it upon 

 the common weeds. The occurrence of this fungus as a disease 

 producing organism is largely dependent upon the conditions, and 

 when by excess of moisture or of heat the plant is placed at a dis- 

 advantage, or the fungus favored, the disease is likely to occur. 



Means of Prevention. 



Little can be said at present concerning special means of preven- 

 tion to be adopted for Rhizoctonia diseases. Plants growing under 

 the most favorable conditions of moisture, temperature, and nutri- 

 tion will probably show marked resistance to the attacks of such 

 diseases, so that good sanitary conditions aiv of the first importance. 

 An excess of moisture and the presence of freshly decaying plant 

 products in the soil will unquestionably favor the disease. Par- 

 ticularly in the propagating and forcing benches is a frequent 

 change of soil advisable. The fungus grows well upon acid media, 

 and liming of tlie soil is therefore well ; but this of itself is not 

 thoroughly effective. If the fungus should become a serious pest 

 in greenhouses, it may sometimes prove practicable to sterilize the 

 soil with steam or with hot water. 



* Atkinson, Geo. F. Some Diseases of Cotton. Ala. Agl. Exp. Sta., Bulle- 

 tin 41, p. 28. 



