14 SOME ASPECTS OF THE INDIGO INDUSTRY IN BIHAR 
The artificial production of wilt. Wilt can be artificially produced in the 
following ways :— 
(a) By mutilation of the root system. 
(b) By cutting back young rapidly growing August sown plants in 
October, when the reserve materials in the tap-root are insufficient for root 
regeneration. 
(c) By October and November cultivation of old indigo dependent for 
its crude sap on superficial roots. 
(d) By complete cutting back in the cold weather, when the root rege- 
neration of surface-rooted types is difficult on account of the low soil tempe- 
rature. 
(e) By waterlogging slowly from below during the rains by closing the 
drainage openings of lysimeters. 
Undoubted wilt has been produced by root mutilation in two cases. The 
first occurred in a plant which was pruned on June 2Ist, 1919. The roots 
were exposed on July 15th, and found healthy in all respects. Before 
replacing the soil, the tap-root was severed at a depth of one foot 
below the surface and most of the fine roots were destroyed. Wilt 
developed. The second example occurred in the case of a plant which was 
pruned on June 21st, 1919. The roots were exposed on August 5th and 
were found to be normal. Before replacing the soil, all the fine roots 
and nodules on the laterals were removed to a depth of one foot but 
the tap-root was left intact. Wilt rapidly developed and when the root 
system was again exposed on August 29th, very few active roots were 
found. 
The complete cutting back, about mid October, of young actively growing 
August sown indigo is certain to result in numerous cases of wilt. In 1914, 
three plots of August sown indigo, each a quarter of an acre in area, were cut 
back about the middle of October. Most of the plants died but a certain 
number produced weak wilted shoots. Root regeneration was found to be 
practically impossible due to the lack of reserve materials in the young roots. 
In another plot, plants with larger roots, when cut back at a later period, shot 
normally. These experiments have been repeated several times since with 
similar results. 
Another method of producing wilt is to cut back tall August sown plants 
during the cold season, when the temperature of the soil is too low for root 
regeneration to take place easily. In December 1918, a number of lines of 
very healthy well-developed August sown plants were cut back when over 
five feet high. It was found the following February that the new growth 
