E. J. BUTLER 17 



inserted under the leaf sheaths^ and in about a month when worms are added 

 to the water in which the plants are growing. AVhen infection comes from 

 the stubble of a previously diseased crop, the period depends on the season or, 

 to be more exact, on the humidity. The following are some of the results 

 obtained at Pusa : — 



(1) Seed broadcasted in a plot, which contained stubble from a diseased 



crop of the pre\'ious season, on March 28th, 1913. Ufra distinct 

 by the first week in August, though some doubtful symptoms 

 were seen as early as May 12th. 



(2) Seed self-sown from a preceding diseased crop in December, 1915, 

 , . and germinated during the first three months of 1916, coming up 



through the rotting stubble. Ufra first clearly seen on July 24th. 



(3) Stubble removed from a diseased plot on December 3rd, 1913, and 



seed broadcasted, returning some of the infected stubble, on the 

 same day. As germination was backward and not sufficient 

 to fill the plot, some plants were transplanted into it in January 

 and February, 1914, and some more seed was broadcasted on 

 March 5th. Ufra was first found in a plant of the first batch 

 - • sown, on June 17th, and was seen in all three batches on July 



10th. 



Thus whatever time the seed is sown at Pusa, between the beginning of 

 December and the end of March, ufra definitely develops (when the infection 

 comes from worms left in the stubble from the previous crop) only when the 

 air humidity rises after the rains break in June. When sown early, there is 

 little growth before March or April in Pusa, but the worm is not able to affect 

 appreciably even small plants until the air humidity rises enough to allow it 

 to climb up the above-ground parts. That there is no inherent inability in 

 the worm to attack rice during this period is evident from the fact that at any 

 time between December and April it has been possible to secure infections in 

 the laboratory by keeping the plants covered by a bell jar. 



It is now easy to understand why it is that, though there is no month of 

 the year during which paddy may not be found growing in some part or other 

 of the infected districts, ufra is confined to the period from June to December. 

 It is practically certain that the worms occur in the water of low-lying areas 

 in the early months of the year, and probably a good many of them reach the 

 growing boro paddy and get carried up or even, since the night dews are heavy 



* " Diseases of Rice," p. 13. 



