HOWARD AND HOWARD 7 
normal root regeneration. Several factors have been discovered which prevent 
the repair of the root system. In indigo cultivation, the chief source of 
damage to the active roots and nodules arises from the complete cutting back 
of the plant.!_ This results in the destruction of practically all the fine roots 
and nodules and root regeneration is necessary before new growth can take 
place. If the absorbing root system is destroyed when the soil aeration is 
poor, when the amount of reserve material in the tap root is insufficient for 
new roots to be formed, or when the soil temperature is too low for growth, 
root regeneration becomes exceedingly difficult and wilt follows. Thus although 
the cause of wilt is the same in all cases, the agents which produce it may be 
different. In considering the incidence of wilt in Bihar, it is necessary, there- 
fore, to understand fully in every case the factors which are concerned in root 
regeneration. If this is done, all the known eases of wilt fall together and 
are capable of a simple explanation. 
As the nodules and active root system appeared to be of particular impor- 
tance in this question, a great deal of attention has been paid thereto. The 
condition of the roots and nodules, however, cannot be determined with pre- 
cision by observation of the above ground portion of the crop. It was neces- 
sary to find some easy method of rapidly exposing without damage the com- 
plete root system including the finer branches and the nodules. This was 
accomplished by the use of an ordinary knapsack sprayer. The results 
obtained by following the root development throughout the year have proved 
of the very greatest value in the elucidation of this interesting problem. 
Root development in Java indigo. 
The development of the root system of the ordinary indigo crop, sown in 
late September or early October, has been examined for several seasons by 
means of periodical root washings. At first, the tap root extends rapidly 
in length and by the beginning of the cold weather practically no large laterals 
are developed. The root system at this stage consists of a long tap root with 
comparatively fine laterals and a certain amount of nodular development. 
During the cold weather, the extent of the active absorbing system is small 
and little or no growth of roots takes place. With the renewal of activity at 
the beginning of the hot weather in March, new absorbing roots are copiously 
developed and the laterals increase in thickness. Nodular development: begins 
1 A large number of root washinys haye been made, at all stages of growth, after indigo 
plants have been cut back to varying extents. Complete cutting back always kills the fine 
roots and most of the nodules. Heavy pruning results in extensive root and nodular 
destruction but not to the same extent as when the plants are completely cut back. 
