ii 
‘ 
( 121 ) 
the liquid remains many months unchanged without the appearance 
of indigo. But if some microbes of the surface-membrane of an 
ordinary indigo-fermentation are added, as also the special active 
bactery of it in an isolated condition, after some hours an abundant 
indigo-formation is observed,” 
I then tried to make from woad (Jsatis tinctoria), in which, 
according to the literature, indican, i.e. the same indigo-producing 
substance as in the other indigo-plants should be present, a decoc- 
tion with which I might repeat the experiment of ALVAREZ. But 
I could, neither by boiling, nor by extraction at low temperature, 
obtain from this plant a sap which remained unchanged at the air. 
Constantly, after a short time, indigo will separate out of it, without 
there being any question of the influence of bacteria or enzymes, 
so that the word “indigo-fermentation”’ would here be quite mis- 
placed. Neither do purposely added bacteria or enzymes favour the 
indigo-formation from woad-decoction. 
Later, however, I was enabled to convince myself that the state- 
ment of ALVAREZ is correct, as well with regard to the decoction 
of Indigofera leptostachya as to that of Polygonum tinctorium '), 
for which latter plant the same fact as described by ALVAREZ, has 
also been established by Morrscu °). 
So it was evident that the indigo-plants must belong to two phy- 
siologically different groups, and I subjected the concerned chromogenes 
to a further examination with the following results. 
1. The Chromogene of the Indigo-plants is Indoxyl or Indican. 
The chromogene of woad is not as is usually accepted indican, 
but the very instable indoxyl C*H7NO. Indigofera leptostachya and 
Polygonum. tinctorium, on the contrary, contain the constant glucoside 
indican, the constituents of which are, in accordance with the 
supposition of MarcHLewski and RADCLIFFE ®), indoxyl and sugar, 
1) Much material of this Zudigofera, as well full grown plants as seeds, I owe to 
the kindness of Mr. van LOOKEREN CAMPAGNE of Wageningen. This interesting plant, 
a native of Natal, has been cultivated, very rich in indican, in the open ground in 
the Laboratory-garden at Delft; at Wageningen several specimens had grown this 
summer to more than 1.5 M. height. 
Polygonum tinctorium comes from China and is, as the woad, in the seed-commerce 
of VILMORIN in Paris. 
2) Sitz.ber. d. Akad. d. Wiss. zu Wien. Math. Naturw. Klasse Bd 107 pg. 758, 1898. 
8) Journ. Soc. for chem. Industry T. 87 pag. 436, 1898; Chem. Centralblatt Bd 
65 pag. 204, 1898. With thankfulness I remember the aid lent me by my 
chemical colleagues HoogEwerrr and Beurens in the determination of indoxyl, 
Q% 
