1916] PARASITIC BHIZOCTONIAS IN AMERICA 379 



Stewart, 125 in reporting the damping-off of alfalfa seedlings in the greenhouse 

 and the crown rot of mature plants in the field, states that "the one causing 

 dampincr-off of seedlings in the greenhouse is different from the one found in the 

 field. When grown on potato agar (slightly acid, neutral, or slightly alkaline), 

 the former produces a conspicuous dark brown discoloration of the medium, whereas 

 the latter discolors it only slightly. This character may bo useful in the identi- 

 fication of the damping-off Ehizoctonia. Such discoloration of the medium is not 

 common among the species of Ehizoctonia." It is interesting to note that the 

 strain obtained from Louisiana causing a damping-off of alfalfa seedlings and a 

 number of other strains showed the same discoloration as the one studied by 

 Stewart. 



On Agar XII. Growth fair. Few loose, erect hyphae, becoming denser and 

 finally forming an indistinct zone. 



" ALTERNANTHERA E. A. C." 



On Corn-Meal Agar. Growth very rapid, but not dense. Mycelium white, 

 loose, aerial, and fine. No zonation. 



On Green-Bean Agar. Growth good. Mycelium tufted and compact, not 

 turning darker. Zonation somewhat distinct at end of third day. Three zones 

 present. 



On Oat Anor. Growth rapid. Mycelium flat, and very compact, forming a 

 mat over the surface. Zonation. 



On Potato Agar. Growth very rapid, with zone formation beginning im- 

 mediately. Mycelium all aerial and growing very compactly. Plate was covered 

 at end of forty-eight hours and showed two distinct zones and one indistinct. 



On Potato-Glucose Agar. Growth rapid; plate covered in forty-eight hours. 

 Mycelium white, loose, and flaky. Zonation. 



On Agar X1J. Growth good. Mycelium white, fine, compact, and somewhat 

 flaky. Zonation. 



. "ALTERNANTHERA E. A. F." 



On the various media this strain produced the same kind of growth in each 

 case as the strain from the cutting bench, except that it grew more rapidly. 



" ASTER" 



On Green-Bean Agar. Growth fair. Mycelium white, loose, regular, joid flat, 

 becoming somewhat tufted. Four zones formed at end of the fourth day. 



On Oat A gar. Growth fair. Mycelium white, loose, flat, and regular, be- 

 coming fluffy and tufted. Like strain "Carnation E. F." Five zones at end of 

 fourth day. 



On Potato-Glucose Agar. Growth slow and poor. Mycelium mostly submerged 

 and turning brown. No zonation. 



On Agar XII. Growth fair. Mycelium white, loose, flat, and regular, be- 

 coming somewhat tufted. Zonation. 



"BEAN" 



On Corn-Meal Agar. Growth very poor; scarcely visible. Mycelium white, 

 fine, somewhat aeiiai. No zonation. 



On Green-Bean Agar. Growth slow. Mycelium fine, aerial, loose, and white, 

 darkening with age. Two zones formed, but not very distinct; otherwise like the 

 strain from carrot. 



On Potato Agar. Growth fair. Mycelium fine, more or less submerged, and 

 discoloring the medium only slightly. No zonation. 



