NATURAL INDIGO 57 



till March 191 3, when the investigations on the agricultural 

 and botanical aspects of the industry were transferred to the 

 Botanical Section of the Agricultural Research Institute, Pusa, 

 which is directly under the Imperial Department of Agriculture 

 in India. 



Much spade-work had to be done at the start, methods for 

 estimating the indican content of the plant had to be worked 

 out, its localisation in the tissues investigated, and estimations 

 had to be made of the percentage of indican in various species 

 of indigo. At the same time numerous manurial trials were 

 carried out, and the progress of the mahai, or fermentation of 

 the indigo plant in the vat, was studied especially with regard 

 to the influence of temperature upon its rate. The results were 

 in many cases very conflicting and difficult to interpret, but 

 recent work has explained many apparent anomalies in them. 

 Before going in detail into these and later investigations it 

 may be as well to outline very briefly the fundamental opera- 

 tions in the preparation of natural indigo. 



The Indigo Plant. — Of this there are various species, the 

 commonest grown in India being Indigofera Sumatrana (Gaertn.) 

 and Indigofera arrecta (Hochst.), The latter was introduced 

 from Java in 1899 by H. A. Bailey, and is now the principal 

 indigo crop in Behar and Assam. These are leguminous 

 plants, and nodules produced by nitrogen-fixing bacteria are 

 found on the roots. Sumatrana indigo is an annual with 

 comparatively shallow roots, whereas Java indigo is a perennial, 

 when under favourable conditions, and its root system is 

 much deeper. It is believed that the Java plant arose as a 

 cross between a Natal species and the original Java or Guate- 

 mala type of indigo. It is made up of a number of types, 

 early flowering ones with comparatively shallow roots, and late 

 flowering types which as a rule have deeper roots. 



In Behar it is customary to sow Java indigo seed for mahai 

 in October. It may be remarked that in the highly calcareous 

 alkaline soils of Behar but few of the properly matured seeds 

 will germinate. This was shown by Bergtheil and Day to be 

 due to the development of a thin cuticular layer outside the 

 cellulose wall of the seed-coat. Such a layer is absent from 

 Sumatrana indigo. In Java, and also in Assam, where this 

 plant is now being grown extensively, the soil conditions are 

 such that the cuticle is not an obstacle to germination. As 

 suggested by Butler, the Java seed is now treated with strong 

 sulphuric acid for a specified time before it is sown in Behar. 



The seed sown in autumn rises to a height of a few inches 

 normally, at which stage further growth is arrested during 

 the cold weather. With the return of warm weather develop- 

 ment is rapid, and by May or June the first cutting — the 



