8 



tions were slightly wounded and then inoculated, the percentage of 

 loss was very high with nearly all the strains studied. When condi- 

 tions (temperature and moisture) were favorable to the fungus, most 

 of the strains studied were able to infect carnation plants as readily as 

 the carnation strains themselves. 



In the majority of cases all strains were able to cause damping-off 

 of various seedlings. There was a great difference in the virulence of 

 strains when inoculated on the same host from which they had been 

 isolated and when Inoculated on other hosts. Only occasionally was 

 there any indication of marked specialization, and in no case was such 

 indication corroborated in succeeding experiments. 



In older plants, a marked difference in susceptibility was found in 

 the different species. As a rule, the root crops were highly susceptible. 

 Herbaceous crops showed a very marked resistance, altho under cer- 

 tain conditions they were quite susceptible. This variability of re- 

 sistance held true for most of the vegetable and field crops other than 

 root crops. Under ordinary conditions, the majority of flori cultural 

 plants were not subject to attacks of Rhizoctonia, altho the mycelium 

 of this fungus was known to be present in the soil or even on the plant 

 itself. 



In a study of these experiments the point that stands out at first 

 glance is the great variation in the mortality of the plants when inocu- 

 lated with strains from the same host and when inoculated with 

 strains from other sources. From the fact that all the strains studied 

 showed the ability to attack the same species of plant and produce 

 the same characteristic symptoms,. it seems clear that they can be in- 

 cluded under one form, Rhizoctonia Solani Kiihn (Corticium vagum 

 B. & C.). These experiments show further that the virulence of R. 

 Solani ( C. vagum) is very variable, as is also the degree of resistance 

 of the various host plants, both depending on a number of varying 

 factors. 



GROWTH ON MEDIA 



Studies of the growth of Rhizoctonia Solani on media show 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 



Measurements of mycelial cells of various strains of RJiizoctonia 

 Solani showed such variation, even with different strains from the same 

 host, that on them, as 011 the growth on media, no conclusions can be 

 based in regard to distinguishing the strains of this difficult species. 



