And college, pusa, for i9i4-is. hi 



Cruciferce (e.g., mustard, cabbage). A good crop of 

 tobacco was raised on a field which had been under cabbages 

 in the previous season and which was known to be infected 

 with 0. indica. Further experiments to test the effect of 

 different chemical manures on the incidence of vw tokra " 

 are in progress. 



(3) Rubber (Hevea). At the request of the Director of 

 Agriculture, Burma, the section undertook the investiga- 

 tion of a disease of Hevea called " black thread " in Lower 

 Burma. The disease is characterized by the appearance of 

 longitudinal black lines in the naked tissue immediately 

 above the tapping cut. These black lines mark areas of 

 disintegration, stretching through the cambium into the 

 wood, and as tapping proceeds they follow the fresh cut 

 down the stem. The flow of latex becomes decreased, but, 

 the most serious aspect of the disease is the failure of an 

 infected tree to regenerate the bark over the tapped area. 



Microscopic examination of the black cracks has, up to 

 the present, failed to demonstrate the presence of any 

 fungus parasite, but in the bark immediately adjoining the 

 infected area hyphse of a fungus often occurred. This 

 fungus was identified as Phytophthora the cause of the 

 : ' canker ' : of Hevea. At the moment of writing the 

 investigation has not been carried further but experiments 

 are in progress. 1 



(4) Sal tree (Shorea robusta). At the request of the 

 Bengal Forest Department the section undertook the 

 investigation of a disease in the sal forests of the Duars, 

 said to be due to a fungus parasite. In the Buxa Division 

 a considerable number of sal trees can be seen in a dead and 

 dying condition. When dead the trees are left standing 

 bare and leafless and in dying trees the foliage is scanty 

 and there are obvious indications of a decrease in vigour 

 of growth. In all the dead and dying trees which were 

 examined there were indications of a fungus attack in the 

 roots. If the main root of an unhealthy tree is laid bare 



1 Infections with pure cultures of this Phytophthora have since been successful 

 in producing this disease on healthy trees. 



