Strains of Rhizoctonia Solani Kilhn. 209 



six were collapsing on the 5th day and all were dead on the 

 8th day. 



With fungus 5 none of the seeds were diseased up to the Sth 

 day. Growth was very feeble, probably due to the medium 

 becoming contaminated by rapidly growing saprophytes after 

 the date of infection. 



The above results compare fa\'ourabh^ with those of the pre- 

 ceding experiment. 



Microscopical Characters. 



Although, as already stated, there are definite distinguishing 

 features between the various forms when compared macro- 

 scopically, under the microscope, however, the differences are 

 confined to the colour of some of the hyphae in old cultures. 

 In cultures of all ages the size of the hyphae varies \\ithin the 

 same limits in all forms. In cultures forty-eight hours old all 

 the h3-phae are h^'aline and those of one form are indistinguish- 

 able from the others. In cultures fourteen days old, some of the 

 forms show the presence of brown hyphae. These are E, I, S, A , 

 PO and PE. On agar the colour of the brown hyphae of the 

 fungus E is somewhat lighter than the others which are of a 

 darker reddish-brown. In the case of B and W all the hyphae 

 when examined singly are hyaline and buff in mass. In cultures 

 seven weeks old on potato the hyphae are a mixture of hyaline 

 and bro\\Ti in E, I, S, A , PO and PE. The hj-phae of B, on the 

 other hand, remain hyaline when examined singly and buff or 

 light brown in mass. This is also the case with W for hyphae 

 proper but the inner tissues of sclerotia are brown. 



CONXLUSIOX. 



As already stated some of the above isolations are easily 

 distinguishable macroscopically ; on the other hand, some of 

 these when examined microscopically cannot be separated from 

 each other by any observable character. The microscopic 

 differences observed in some cases are only shght and it is 

 considered that they do not justify a multiphcation of species. 

 Such minor differences have been observed in the case of several 

 other species of fungi with the result that they have been split 

 into biological species of the same morphological species. 



Matz(:2) has separated into different species of Rhizoctonia 

 isolations which differ between them considerably less than the 

 two extremes / and B forms mentioned above. The minor 

 differences described by Matz occurred in some cases when 

 the fungi were growing on different media and if this method of 

 determination of species were followed in this paper, the fungus 

 E growing on freshly prepared agar would be a different species 

 from E growing on the same medium wiiich had been allowed to 



