INSTITUTE, PUSA, FOR 1919-20 49 



in drained and undrained lysimeters, to the monthly ex- 

 amination of root-development, and the continuation of 

 work on seed-selection. 



Lysimeter experiments. According to the investiga- 

 tions of the Howards, indigo-wilt is nothing more than the 

 effect of waterlogging and consequent lack of aeration. 

 When there is heavy and continued rainfall, the water-level 

 rises and the soil becomes waterlogged, the air supply to the 

 growing roots and nodules of the plants is cut off, and the 

 roots, consequently, cannot thrive. Hence the new roots and 

 nodules begin to die off below and wilt appears above. 



Evidence of this has been obtained by growing indigo 

 plants in cemented lysimeters, provided with drainage open- 

 ings. In cases where the openings were closed, all the plants 

 in the lysimeter got wilt, even when growing in soil which 

 was rich in phosphate, and those with free drainage all es- 

 caped, even when they were growing in a soil poor in phos- 

 phate. Observations on these plants growing in lysimeters 

 are being continued for the second year, and the effect of 

 drainage on the growth and the health of plant is still 

 under observation. Field observations have afforded further 

 evidence. The first sign of wilt in the Pusa Botanical Area 

 appeared last year (1919) in the third week of July, i.e., 

 when the water-level was highest. When the water-level 

 went down, aeration was regained to some extent and the 

 plants began to improve. The water-level rose again in the 

 first week of September, and again wilt appeared. 



Root-development. Systematic monthly examination of 

 root systems is being continued. It is found that the 

 nodule and new-root formation begins in April, but up to 

 the break of the rains their formation is very slow. Soon 

 afterwards, they begin to grow quickly. When the water- 

 level begins to rise, new roots and nodules are formed 

 towards the surface, and the older, lateral roots begin to 

 change their direction, turning upwards, till by the end of 

 July their tips reach very near the surface of the soil, and 

 almost all new roots and nodules are found in the upper 

 three inches. Weak plants which cannot form new roots 



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