1016] PARASITIC RHIZOCTONIAS IN AMERICA 329 



plants, causing a crown rot. In one or two cases several leaves were 

 completely rotted at the crown. 



POINSETTIA, Euphorbia pulcherrima 



About October 7, 1912, young poinsettia plants were taken from 

 the cold house (50 to 60 C.) of the flori cultural greenhouses and put 

 in a box with a glass top. They were then placed near the cutting 

 bench, in which a number of plants of various kinds were damping off. 

 The poinsettia cuttings shortly afterwards began to die off rapidly. 

 The characteristic lesions on the stems of the young plants and pure 

 cultures of the diseased material indicated that this condition was due 

 to R. Solani. The lesions, instead of being on one side and more 

 or less localized, in almost every case formed a collar around the stem 

 at the surface of the soil. The collar was about 2 to 3 millimeters 

 wide, somewhat depressed, and of a dark color. Strands of the brown 

 mycelium were visible spreading over the soil in the pots. This infec- 

 tion probably had its origin in the cutting bench. 



POTATO, Solanum tuberosum 



On the potato R. Solani exhibits a number of interesting charac- 

 teristics, which vary with climatic conditions, age of the host, and part 

 of the plant attacked. 



The sclerotial stage of this fungus has been observed on practically 

 every Illinois potato tuber examined by the writer. Moreover, in 

 every shipment from other states which has been examined, the fun- 

 gus has been found present. The tubers affected were dotted with 

 brownish black sclerotia of various shapes and sizes (Fig. 15), but so 

 far as could be determined, they were causing no direct injury. This 

 type of Rhizoctonia disease of potato is the one most commonly found 

 in the United States. 



R. Solani also causes, under certain conditions, a russeting, or 

 scab, a cracking of the tuber, the formation of pits at or near the len- 

 ticels, and a wet rot of the tuber. These types of injury have been ob- 

 served by Rolfs 92 ' 93 in Colorado, by Orton 73 in various states, and 

 by Morse and Shapovalov 69 in Maine. 



On the plant itself this fungus produces various types of diseases. 

 In many cases young plants are completely cut off before they reach 

 the surface of the ground. Older plants that are severely attacked 

 just below the surface of the ground usually die off quickly. If they 

 are only slightly attacked, the fungus produces small lesions on the 

 stems, the plants take on a dwarfed and unhealthy appearance, and 

 the tubers remain small, altho the plants usually live thru the sum- 

 mer. When the stem is girdled by the fungus so as to prevent trans- 

 location entirely, large tops are produced, aerial tubers are formed, 



