110 BA E AS A PARASITE IN BIHAR 



infected with " tokras," was solected for experimental work. This area was 

 divided up into six equal plots (A, B, 0, D, E, F), each about Triyth acre, and 

 chemical manures were applied as indicated on the plan (Text-figure 1). 



On /^he 6th October, 1914, the mamire was spread evenly on the surface 

 of the soil and mixed with the soil with a khurpi, a light beam harrow was then 

 run over the surface. Tobacco (Nicoiiana tahacum) was planted out in all the 

 plots during the following fortnight. 



In spite of the fact that the land was known to be badly infected with 

 " tokra," a fair crop of tobacco was obtained and there were very few 

 " fcokras." Both 0. indica and 0. cermui occurred, but their incidence did not 

 appear to be in any way affected by the application of the manures. The 

 total number of "tokras" in the tobacco was about twenty, although in the 

 previous year when the land was under cabbages they were to be counted by 

 the thousand. The " tokras " which occurred on the cabbages were, of course, 

 0. indica, the common "tokra" of Brassicas, and the explanatioii of the 

 relative immunity of the tobacco, during this first season, seemed to be that 

 this species was not a serious parasite of tobacco. This coincided with observ- 

 ations in the fields round Pusa where, although 0. cernua usually prevailed on 

 the tobacco, a certain amount of 0. indica could nearly always be found. 



(2) PusA— Season 1915-16. 



The same land was placed under tobacco, mustard and cabbage as indi- 

 cated in the Text-figure 2. (See p. 111.) 



' (a) Tobacco. The two northern plots (A and B) were planted with tobacco 

 {N. tabacum) ; each plot contained 18 rows with 16 plants in each row. Of 

 the two plots under tobacco the one on the western side (A) was manured 

 with sodium nitrate. Instead, however, of mixing the nitrate with the soil 

 before planting out, the manure was dissolved in water and given to each plant 

 in solution. Each tobacco plant received 1 oz. of sodium nitrate, given in 

 three doses at intervals of 7 days, during the later portion of November ; in 

 all about 18 lb. of sodium nitrate was distributed among 288 tobacco plants 

 in an area of -}^t]i acre. This works out at a rate of about 3 cwt. per acre. 

 The first " tokra " appeared in the unmanured plot in December, but by the 

 middle of January plants were appearing in both plots. The tobacco was 

 cut on March 13th and the amount of -'tokra " counted with the following 

 results : — 



