HOWARD AND HOWARD 9 
November and December after flowering sets in. During the cold weather, the 
roots of seed plants show few active rootlets and extensive regeneration does 
not take place till the temperature of the soil rises in March. 
In both the ordinary and the seed crop, therefore, the features of the root 
system may be summed up as follows :— 
(1) The periods of intense nodular development are at the break of and 
during the early rains and, in the case of the seed crop, in September and 
October. 
(2) Temperature, soil aeration and moisture are the chief factors in the 
formation of absorbing roots and nodules. 
(3) Although the nodules and fine roots are easily destroyed, the main 
tap-root and the larger laterals possess remarkable vitality and are capable 
of remaining dormant in the soil without damage from December to March, 
after which they often produce a new set of absorbing roots and nodules. 
Observations and experiments on the cause of wilt. 
The evidence on which we have based our conclusions as to the cause of 
wilt has been obtained by several methods. The root systems of numerous 
healthy and wilted plants have been compared in detail, the occurrence of 
wilt in Bihar has been studied under various conditions extending over many 
years, actual cases of wilt have been produced artificially in no less than five 
different ways while many examples of recovery have been closely examined. 
The conclusions arrived at, as a result of these experiments and observations, 
have been confirmed by a study of the behaviour of other crops during the 
rains at Pusa and also by the growth of indigo, on soils differing widely as 
regards aeration, in other parts of India. 
The root systems of wilted and healthy plants. The roots of a very 
large number of wilted plants have been exposed by the spraying machine 
and compared with those of healthy plants. The results have always been the 
same. Where the wilted condition is well marked, healthy nodules are never 
found while the number of active roots is exceedingly small. Dead and dis- 
coloured fine roots and nodules are, however, abundant. In the case of the 
roots of healthy plants examined at the same time for comparison, there have 
always been abundant fine roots and root nodules in an actively growing 
condition. Indigo wilt is, therefore, associated with the recent destruction of 
the absorbing root system. 
In the rains, wilt occurs on deep-rooting types to a much greater 
extent than on those with a shallow root system. Java indigo, as grown 
in Bihar, is an exceedingly mixed crop and consists of a large number of 
