Sick Soils 



21 



bicolor, A. wilkesiana, var. tricolor; A. wilkesiana, 

 var. marginata, Ageratum mexicanum, Alyssum odor- 

 atum; Coleus, Cuphea phatycentra, Tresine, Petu- 

 nia, Piguerua trinervia, Lautolina chamoecyparissus, 

 Sedum spectabile, Althernanthera, Vincia major. 



The Organism, In the United States the first ex- 

 tended account of Rhizoctonia was given by Pam- 

 mel.* Many other excellent accounts by American 

 workers have appeared from time to time, to which 

 we shall have occasion to refer later. 



The genus Rhizoctonia includes several forms of 

 sterile fungi, all of which are distinguished by the 

 manner of growth in pure culture, and by its myce- 

 lium. Young hyphse of R. solani Kuhn are at first 

 hyaline, then deepening in color from a yellowish to 

 a deep brown. The young branches are somewhat 

 narrowed at their point of union with the parent 

 hyphse and grow in a direction almost parallel with 

 each other. A septum is also laid down at a short 

 distance from the point of union with the parent 

 mycelium (fig. 3, d and e.). There is another form 

 of hypha which is made up of barrel shaped cells 

 (fig. 3, f.), each of which is capable of germinating 

 like a spore. In pure cultures R. solani produces 

 sclerotia which are first soft, whitish, and which 

 later become hard and dark. The fungus is, carried 

 over from year to year as sclerotia which are able 

 to withstand the effects of heat, cold, drought, or 

 moisture. 



♦Pamrael, L. H., Iowa Agr. Expt. Sta., Bui. 15: 244-251, 1891. 



