272 DOWNY MILDEW OF BAJRI AND JOWAR. 



by a germ-tube and not by zoospores. These observations were 

 made for two years, 1910 and 1911, at the kharif and rabi seasons, 

 at different places and on several individuals of each host, and the 

 differences were quite constant. 



Further, I made cross-inoculations of both these Sclerosporas ; 

 bajri plants were inoculated with the conidia of the jowar Sclerospora 

 and jowar plants with zoospores of the bajri Sclerospora. No 

 infection took place in either case. In order to test this point 

 further, a few affected young bajri plants were transplanted in a 

 jowar plot and a few affected jowar plants in a bajri plot. In both 

 the cases the affected plants grew with disease on them while their 

 neighbours did not take the disease at all. 



One reason for the failure of cross-inoculation might of course 

 be that, as noted above, infection probably occurs at the seedling 

 stage and not after. It is also possible that the two forms are 

 each adapted to its own host like " biological forms." 



These observations go to show that the bajri and jowar Scleros- 

 poras are not one and the same fungus. They differ in their mode of 

 attack and hence in the field characters of the diseases. Although 

 the first form of attack, which occurs probably at the seedling 

 stage, is common to both bajri and jowar, the 2nd and 3rd forms are 

 peculiar to jowar alone. The malformations of the heads found in 

 bajri never occur in jowar and the leaf -shredding which is so marked 

 a character on jowar is much less common on bajri. Each form is not 

 only fixed to its host but has modified morphologically also to a 

 certain degree. These differences seem to me to justify us in regard- 

 ing the two forms as two distinct varieties, if not species, and the 

 following key is suggested for identification. 



Sporangia broadly elliptical, with a papilla at the free end and 

 germinating by zoospores Sclerospora graminicola. 



Sporangia sub-orbicular, with no papilla at the free end and 

 germinating as conidia by a germ-tube . . . . S. gramini- 

 cola var. Andropogonis Sorghi. 



The way in which the fungus lives from year to year is still a 

 mystery. The conidia lose their vitality after three or four hours. 



