120 OROBANOHE AS A PARASITE TN BTHAR 



The distribution of the "tokra " in the manured and unnianured plots 

 was the same as in last year ; the southern (niamired) plot (M) had the 

 smaller amount of "tokra." 



Tobacco. Tobacco was planted out in the two plots next to the mustard 

 as in the previous season, the number of plants in each plot being increased 

 in 1916-17 from 288 to 342. The nitrate was applied to the same plot as in 

 the season 1915-16 but was given in solution at the rate of 1 oz. to each plant. 

 The total quantity of nitrate used thus came to about 22 lb. 



" Tokra" appeared at the end of November and continued to come up 

 until the crop was cut on 26th February, by which date the tobacco was in a 

 very bad condition. The actual amounts of "tokra" present were as 

 follows : — 



Number of Number of Number o i 



tobacco plants 0. cernua 0. indica 



Manured (S) .. 342 17,291 442 



Unmanured(P) .. 342 14,822 981 



In comparison with the previous season the total amount of 0. cernua 

 shows an increase in both plots, the larger quantity being, as in the previous 

 season, in the manured plot ; the increase, however, is proportionately greater 

 in the unmanured plot. The amount of 0. indica present shows the decrease 

 which has already been mentioned as occurring in all the experiments in the 



season 1916-17. 



III. POT CULTURE, 1916-17. 



The fact that the tobacco grown at Pusa in a field which was known to be 

 infected with seed of 0. indica suffered from " tokra " only very slightly in the 

 first year, and in the second year contained far less 0. indica than the adjoining 

 plots of mustard and cabbage, in conjunction with the fact that one field of 

 tobacco outside Pusa was found to be practically destroyed by this species, 

 suggested that the morphological species 0. indica possibly contained two 

 races differing in their parasitic properties. 



With a view to testing the parasitism of 0. cernua and 0. indica on different 

 hosts, with greater accuracy than was possible within the limits of a field 

 experiment, a series of pot cultures was made at Pusa during the cold weather 

 of 1916-17. Soil for the pots was obtained from land which had been lying 

 fallow for a large number of years, and which was not known to have ever 

 been under a crop Uable to the attack of Orobanche. There was therefore a 

 strong probability that such soil would not contain any seed of Orobanche and 

 moreover a number of the pots, filled with a mixture of leaf-mould and this 

 soil, were sterilized in the steam sterilizer in order to kill any chance seeds 



