Strains of Rhizoctonia Solani Kiihn. 201 



Media. The above forms of Rhizoctonia Solani have been 

 growTi for se\eral months, and in some cases for over two vears 

 on different kinds of hqiiid and sohd media inchiding the fol- 

 lowing: steamed potato, steamed turnip, steamed carrot, prime 

 agar, potato agar, malt extract agar, boiled rice, malt extract 

 gelatin, milk, carrot extract, turnip broth, bouillon, apple 

 extract, Xaegeli's solution, Ufchinsky's solution, and malt extract. 



All fomis grew well on all the sohd media but growth was 

 feeble and slow on most of the hquid media, particularly 

 bouillon, apple extract, Xaegeh's solution, and Ufchinskv's 

 solution. Of the hquid media the best growth was obtained on 

 milk and tuniip broth. Xone of the fungi grew well on any 

 medium which was unsuitable to the others, and the best mediuiii 

 for all was steamed potato. 



Macroscopic Characters. 



WTien grown on the above media it was observed that in some 

 cases there was considerable variation in the colour, amount of 

 aerial growth and the size and number of the sclerotia, within 

 the one form. In spite of this, however, it was possible from 

 certain characteristics of growth to distinguish some of the forms 

 from others, and these diagnostic features were retained through- 

 out. The two extreme cases were / and B, since the fonner 

 produced sclerotia wliich were darker, more discrete, and more 

 even in size than any of the other fornis ; the latter, on the other 

 hand, did not produce a single sclerotium on anv mediimi. Like 

 the other sclerotia-producing forms, / produced larger and a 

 greater number of sclerotia on media like steamed potato, 

 carrot and turnip than on agar and gelatin compounds. Pre- 

 \-ious experiments \\ith E have sho\Mi that this is due to the 

 fact that the former media retain moisture for a longer period 

 and allow of better aeration \\ithin the mediimi itself than is 

 the case with agar and gelatin. For these reasons the fungi are 

 able to continue gro\\'th for a much longer period. The growth 

 of the mycehum is confined to the surface layer on agar and 

 gelatin and does not penetrate deeply into the medium o^^■ing 

 to the absence of oxygen. This is probably also the reason wh\' 

 the fungi do not grow so well on hquid media. All the sclerotial 

 forms produced larger sclerotia on fresh agar medium than on 

 the same medium wliich had become slightly dry. If the dried 

 agar medium is melted, cooled, and a subculture made 

 immediateh" afterwards, sclerotia are fonned wliich are of the 

 same size as those produced on freshly made medium. This is 

 due to the fact that moisture in the form of drops of water on 

 the sides of the tubes or Petri dishes is favourable to their rapid 

 and continued growth. This sensitiveness to the presence of 



