370 .BULLETIN No. 189 [June, 



was found with the growth on potato-glucose agar. On both these 

 media zonation was usually lacking or indistinct. 



On Agar XII most of the strains grew rather poorly and produced 

 a white, flaky growth, with varying zonation. 



Early in the study of the characters of the strains on culture 

 media, it was noticed that as there were characteristic differences in 

 growth, so also were there differences in the production of sclerotia. 



The strains "Eggplant I," "Lettuce," " Chenopodium, " and 

 "Thistle" on green-bean agar all iormed sclerotia in a characteristic 

 manner. The sclerotia were white at first and flat, later turning black, 

 and as the culture became older, curling up and becoming crust-like. 

 All four of the forms mentioned above showed these same character- 

 istics, altho they were originally obtained from widely separated locali- 

 ties. (See Fig. 22.) The strain from onion produced sclerotia which 

 were entirely different from those of other strains in that they were 

 small (.5 to 1 millimeter in diamater), perfectly round, bright colored, 

 and developed submerged in the medium. (See Fig. 23.) The strains 

 "Buckwheat," "Carnation R.O.," " Gypsophila, " and "Sedum" 

 rarely produced sclerotia in culture. Kepeated observations showed 

 that this loss of power to produce sclerotia was the first sign of the de- 

 generation and loss of virulence of the strain. 



All the other strains studied produced sclerotia which were at first 

 white, later becoming brown. Altho the sclerotia from the strain from 

 potato are similar to those from carnation when grown on culture 

 media, on the potato tuber they are entirely different. For the most 

 part the Khizoctonia sclerotia on potato tubers which the writer has 

 examined are flat and hard, have a black luster, and are in many re- 

 spects like the sclerotia produced in culture media by the strains from 

 eggplant, lettuce, etc. 



The only conclusion that can be drawn from this study of the 

 growth of Khizoctonia Solani on media is that the strains are very 

 variable, those from the same host often producing a different growth, 

 even? on the same media, and that the differences in various cultural 

 characters which are shown by strains from different hosts are no 

 greater than differences which may be manifested by two different 

 strains isolated from the same host or by the same strain at different 

 ages. 



MEASUREMENT OF MYCELIAL CELLS 



It was rather difficult to choose a standard in the measurement of 

 the mycelial cells, because the cells varied in size at different ages and 

 on different media. Finally the following standard was chosen: 

 Hyphae from the outer edge of a twenty-four hour old culture on 

 green-bean agar were selected at random. The length and width of 

 a cell from which the branch arose nearest the tip of the hypha, and 



