INDICAN 251 



/. tinctoria, and 7. sumatrana, but also in other plants, such as 

 Isatis tinctoria, Polygonum tinctorium, species of Phajus and 

 other orchids, e.g. Calanthe and Strohilanthes. Although the 

 woad plant, Isatis tinctoria, also yields indigo, the substance 

 giving rise to the dye is not identical with the indican of 

 other indigo yielding plants. According to Beijerinck * the 

 precursor in the plant is a substance isatan, of unknown 

 composition. In the plant, indican is well distributed in the 

 aerial organs. Thus in Indigofera it is found in all the tissues 

 of the leaf except the tracheae of the xylem ; it is also abun- 

 dant in the apex of the stem in all tissues except the wood 

 vessels and the laticiferous system. The flowers also have a 

 small quantity, but the root is characterized by its absence.f 

 At one time it was considered that the chloroplasts played 

 an important direct part in the formation of indican, but Leake 

 can find no evidence of this. 



Identification. 



1. The tissue may be boiled in a 2 per cent solution of 

 ammonia. The addition of chloroform to the filtered extract 

 may be made to separate the indigo ; the chloroform will sink 

 to the bottom of the solution, carrying with it the indigo. 



2. Tissues containing indican on exposure to the vapour 

 of alcohol for twenty-four hours will turn blue ; the reaction 

 will be better marked if the chlorophyll be subsequently dis- 

 solved out with absolute alcohol. 



3. The tissue, in bulk or in section, may be boiled in 

 strong hydrochloric acid and ferric chloride added. The in- 

 digo will separate out. 



4. The tissue is cut up into pieces and quickly immersed 



in the following mixture : — 



Glacial acetic acid . . . . 2 c.c. 



Strong sulphuric acid . . . . i ,, 



Ammonium persulphate . . . '5 gram. 



Water to ..... . loo c.c. 



As this fluid penetrates the cells, the indigo is precipitated in 

 blue granules. When penetration is effected fully, the material 



♦Beijerinck: " Broc. Kon. Ak. Wet. Amsterdam," 1900, loi ; see 

 however, Marchlewski : " Ber. deut. chem. Gesells.," 1902, 35, 4338. 

 t Leake : " Ann. Bot.," 1905, 19, 297. 



