1^ J. 1^ SHAW. Il9 



with reference to these four hosts that the existence of physiological 

 races of the fungus was investigated. As it became evident in the 

 course of the research that more than one species of Bhlzoctonia 

 was present, it will be convenient to consider the results in two parts. 



Rhizoctonia solani, Kuun. 



Jute. — Rhizoctonia has been known for some time as the cause of 

 a destructive disease of seedhng jute, the symptoms being very sim- 

 ilar to those caused by Pi/thium iu other plants. Seedhngs attacked 

 by the disease show at first a slight yellowish patch just above the 

 ground level ; after a time this darkens and the tissues soften and 

 collapse, the whole seedling falhng to the ground (PI. I, Figs. 3, 4). 

 Young seedlings from one to two inches high are extremelv suscep- 

 tible to the disease. 



In some cases plants a good deal older than this were found 

 infected with the fungus. In October 1910, several mature plants 

 in the jute plot at Pusa showed the disease ; these plants were from 

 6 to 8 feet high and could easily be distinguished from their healthy 

 companions by their withered leaves and blackened stems, the 

 blackening being most marked at the base near the ground level. 

 In 1911 the jute was sown on a different area, which had been left 

 fallow during the previous season ; there was very little disease in 

 the crop and only a few infected plants could be found. One of 

 these is shown in PI. I, Fig. 1 ; the blackened infected area at the 

 base of the stem is clearly visible. In a transverse section through 

 this region the whole of the outer tissues of the stem appear rotted 

 and broken down and in some cases hyphee can be seen entering the 

 wood (PL XI, Fig. 2) ; sclerotia occur in the decaying cortex. From 

 diseased j)laiits, such as these, cultures were obtained on agar 

 medium E (see Appendix) and produced first a growth of white 

 hypha3 and then numerous small black sclerotia. 



In the jute districts of Eastern Bengal Rhizoctonia causes a 

 certain amount of damage. Mature plants infected with the fungus 

 have been collected in both the Mymensingh and Rangpur districts. 

 In some years the damage to the seedling crop is extensive in certain 



