46 REPORT OF THE AGRICULTURAL RESEARCH INSTITUTE 



area, but that if all the stubble is removed, a healthy crop 

 can be grown. Furthermore it has been shown that the 

 parasite can extend along the water courses, both with and 

 against the stream, and infect neighbouring plots, but the 

 distance travelled has hitherto been small. When atmos- 

 pheric humidity within the crop is low, extension is hin- 

 dered, but provided the humidity conditions are right, new 

 case's of disease may become evident even on large plants 

 within a month and many plants may be destroyed within 

 two months of liberating the parasite in the water supply. 

 Though under normal conditions the parasite passes into a 

 dormant condition in the rotting stubble in the interval 

 between successive crops (say from December to April), it 

 can be kept in an actively parasitic state through this period 

 by supplying it with constantly renewed young growing 

 paddy for food, and this fact may increase our difficulties 

 in dealing with it where the crop known as boro paddy is 

 grown, fortunately a relatively small area. On present 

 information it seems probable that the boro crop harbours 

 the parasite, but that the low atmospheric humidity during 

 the winter and spring months, when this crop is growing, 

 checks extension and perhaps also interferes with the multi- 

 plication of the parasite. It is this same factor that doubt- 

 less explains the relatively little damage caused to the early 

 (aus) crop and to the main crop in its early stages; experi- 

 ments at Pusa have shown that so long as the above-ground 

 parts of the plant are maintained dry, it is difficult to get 

 successful infections, even though the roots and base of the 

 plant are in mud and water, whereas during the monsoon 

 or when inoculated plants are covered by'bell jars, infection 

 readily occurs. When insufficiently provided with mois- 

 ture the parasite tends to pass into a dormant condition and 

 ceases feeding. 



Laboratory work was directed to attempts to establish 

 conclusively that the cause of the disease is Tylenchus 

 angustus, the eelworm described in Bulletin No. 34 of 1913. 

 Attempts to obtain it in pure culture failed but conclusive 

 proof was ultimately got by a series of experiments which 



