64 SCIENCE PROGRESS 



amounting to absolute proof, however, that the indican content 

 is related to root-nodule formation in the sense that high 

 indican accompanies high nodule activity. It is, however, 

 proved conclusively that cultural and manurial conditions 

 may cause very great alterations in the indican content. 



More recently Davis has shown that the percentage of 

 indican in the leaf appears to be determined mainly by the 

 amount of readily available nitrogenous substances in the soil. 

 When this is high the indican content is low. If grown on a 

 good soil, with a cover crop of wheat, such as Pusa 4, a plant 

 rich in indican is obtained, as the wheat removes nitrogenous 

 compounds from the soil. This is effected by sowing two rows 

 of wheat between each row of indigo. The wheat is reaped in 

 the spring and the indigo, which grows but little in winter, 

 comes on well after its removal. This method of sowing with 

 a cover crop was previously recommended by Howard and 

 Howard, but in the present poor conditions of planters soils 

 may not be practicable, though successful at Pusa. 



Effect of the Variety of Indigo Plant upon Indican Content. 

 — ^Though large alterations are induced in the indican content 

 by external conditions, yet Bergtheil showed that each variety 

 of the Sumatrana plant studied at Sirsiah had an average 

 indican content in which it might differ from other varieties. 

 Differences also occur during the growth of each individual 

 plant, as the indican content increases with age up to a certain 

 point, but decreases during seed formation. It has been 

 found that Java indigo has a higher indican content than 

 other species, yet on one occasion, at Pusa, Java indigo gave 

 0-6-0-7 per cent, indigotin and Sumatrana gave o-8. It may 

 be remarked that, while the plant contains the glucoside indican, 

 the results of analyses are usually given as indigotin. 



Among the Java plants there are certain very obvious 

 differences, such as colour of stem — red, reddish; or green ; shape 

 of stem — round or angular ; leaf colour — dark or light ; number 

 of pairs of leaflets ; pulvinus — fine or coarse. Though this is 

 so, Parnell concluded that the " morphological examination 

 gives no indication of indigo content, and all work on this 

 character must be controlled by chemical analysis, in spite of 

 its tedious nature." 



Parnell further studied the curves got by plotting indigo 

 content against numbers of individuals. From the positions 

 of the maximum values he concluded that in an ordinary Java 

 crop there would seem to be a number of races differing with 

 regard to their inherent indigo-producing power. " There are 

 two major groups averaging about 10 per cent, higher and 

 lower respectively than the average of the whole crop, and 

 two minor groups averaging about 20 to 25 per cent, higher 



