333 



xyl, I cannot decide. Indigo-red I could also find in the indigo made trom indican, 

 whether chemically by boiliiig with acids, or by bacteria, or by enzymes. Coiiso- 

 quently, if two indoxyls should exist, there should also exist two indicans. 



2. Demonstration of Indigo in the Indigo-plants titemselves. 



For the demonstration of indigo in the plants themselves, Mr. Molisch described 

 in 1893 his » alcohol-experiment « to which he afterwards repeatedly recurred '). In 

 this experiment the parts of the plants to be examined are exposed, in a confined 

 atmosphere, to alcohol- or chloroforni-vapour, for instance by putting them into a 

 glass-box, in which a small vessel with these substances is placed. Thus slowly dying 

 all the indigo-plants become more or less blue, which is perceptible after the chloro- 

 phyll has been removed by extraction with alcohol. I found, however, that never all 

 the present indoxyl or indican changes into indigo. The »alcohol-experiment« suc- 

 ceeds the best with Polygonitm tinctorium, where at least most of the indoxyl changes 

 into indigo. For woad the result is greatly dependent on the length of time which the 

 experiment requires, even on the season, hut invariably only a part, though it may 

 be a great part, of the indoxyl passes into indigo. With Indigofera only a little indigo 

 precipitates in the youngest leaflets and buds, while the older leaves become quite co- 

 lourless by the alcohol-extraction though they are extremely rich in indican, so that, 

 for this plant, the »alcohol-experiment« is without any value ^). 



For woad, as an indoxyl-plant, the alcohol-experiment can be improved by chan- 

 ging it into an »amoniac-experiment«, by which the percentage of indigo is much 

 heightened. If near the woadleaves in the glass-bo.x a vessel with ammoniac instead 

 of alcohol is placed, death follows almost instantly. The leaves then first become of an 

 intense yellow and afterwards, by the indoxyl-oxidation, of a deep blue colour. By 

 subsequent extraction with alcohol the leaves become deeply blue as compared to 

 the lightly coloured »alcohol-leaves«. The »ammoniac-experiment« proves that »ll 

 growing parts of the woad, even the ruots, the rnotbuds'), the cotyledons and the 

 hypocotyl, contain indoxyl. 



The explanation of the »alcohol-experiment« is, of course different for the diffe- 

 rent indigo-plants. This explanation must at the same time elucidate the following 

 fact: Suddenly killed leaves, fnr instance leaves, which have been kept in vapour of 

 100° C, do net colour at the air, neither of woad, nor of Polygoniim, nor of Indigo- 

 fera, why then do they become blue when slowly dying off? 



') -Sitzungsber. d. k. Akad. d. Wiss. zu Wien, Bd. 102, Abt. I, pag. 269, 1803; Bd. 107. 

 pag. 758, i8q8, and Berichte d. deutschen Botan. Gesellsch., Bd. 17, pag. 230, 1899. 



') Quite wrongly Mr. Molisch declares: »Die pracisesten Resultate erhalt man 

 bei Indigotera mit der ,Alkoholprobe'«, and as wrong is his assurance »Durchwegs war 

 zu bemerken, dass die in Europa gezogeneh Pflanzen (von Indigofera) auflfallend viel 

 weniger Indigo liefern wie die tropischen» (Berichte d. deutsch. Botan. Ges., Bd. 17, 

 pag. 231, 1809). 



') The production of leafbuds on the roots of the woad seems nowhere cise men- 

 tioned. Other biennal Cruciferae produce also rootbuds, for exemple Brassiat oleraceu 

 Sisymbriuni atliaiia and Lunarin hicnnis. 



