E. J. BUTLER 



15 



it does even though the boro fields may adjoin badly diseased fields of aman 

 paddy. There cannot be the slightest doubt, from what I have seen, that 

 boro fields are often contaminated with infected stubble from the aman crop. 

 The boro is transplanted into these fields usually within a month of the aman 

 harvest, and the fields themselves usually occupy the lowest land, bounding 

 the banks of the permanent hhils or waterways that run through the centre 

 of the rice hits along the natural drainage lines of the country. Around them 

 are great stretches of land suitable for the deep-water aman in which ufra is 

 most prevalent. As the boro fields are kept permanently flooded, and as 

 some of the infected aman stubble must certainly find its way into them, their 

 water must contain free-swimming worms. Experiments carried out at Pusa 

 have proved that the parasite is only too ready to attack paddy at this period, 

 provided the moisture conditions are kept suitable. Hence there must be some 

 explanation connected with the conditions of the environment to account for 

 the general escape of the boro cultivation. This explanation is to be found 

 in the dryness of the air between February and May as compared with that 

 of the rest of the year. 



The foiiomng table, abstracted from data collected by the Meteorological 

 Department {hid. Meteoro. Memoirs, XXII, p. 460), give.j the monthly normals 

 of relative humidity at a series of stations in or at the borders of the infected 

 area : — 



Monthly normals of relative humidity. 



In all stations the maximum rise in humidity (5 or 6 per cent.) takes place 

 between May and June, and in none (except Noakhali in February) does the 

 humidity between February and May reach 85 per cent. Between June and 

 September the humidity remains above 85, except in Goalundo, where it falls 

 to 84 in September. It may be added that heavy night dews persist after the 

 rains until well into February, but thereafter diminish and disappear as the 

 hot weather sets in. Since the records are taken at 8 a.m., it is probable that 



