( 126 ) 
For woad, as an indoxyl-plant, the alcohol-experiment can be 
improved by changing it into an „amoniac-experiment’”’, by which 
the percentage of indigo is much heightened. If near the woad- 
leaves in the glass-box 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 all growing 
parts of the woad, even the roots, the rootbuds 1), the cotyledons 
and the hypocotyl, contain indoxyl. 
The explanation of the ,alcohol-experiment” is, of course different 
for the different indigo-plants. This explanation must at the same 
time elucidate the following fact: Suddenly killed leaves, for instance 
leaves, which have been kept in vapour of 100° C., do not colour 
at the air, neither of woad, nor of Polygonum, nor of Indigofera, 
why then do they become blue when slowly dying off? 
The answer for Polygonum and Indigofera lies partly at hand. 
By the temperature of the boiling-point, the indigo-enzyme has 
been killed, so the indican can no more be decomposed. If slowly 
dying, on the contrary, the indigo-enzyme can become active 
and indoxyl is formed). But the explanation of the second part 
of the process, that is the transformation of indoxyi into indigo, 
— at the same time the only point which for woad, as an 
indoxyl-plant, requires our attention, — is less clear. I think that 
the course is as follows. In slowly dying leaves the indoxyl changes 
into indigo-blue, because, in this form of death of the cells, some 
alkali originates. In suddenly killed leaves, on the other hand, 
alkali-formation does not occur, they do not grow blue, and the 
indoxyl disappears in another way. 
If in the leaves of indigo-plants the presence of an oxidase, 
acting on indoxyl, could be demonstrated, this would certainly explain 
quite well the action of higher and lower temperatures. But, as I 
said, I could not convince myself of its existence, so that I am 
necessarily led to the alkali-hypothesis. 
The cause of the great lack of indigo-blue which, as above obser- 
ved, diminishes the value of the ,alcvhol-experiment’’, lies in the 
') The production of leafbuds on the roots of the woad seems nowhere else men- 
tioned, Other biennal Cruciferae produce also rootbuds, for ‚exemple Brassica oleracea, 
Sisymbrium alliaria and Lunaria biennis. 
2) Also a slow death of the leaves by drying or by frost renders the protoplasm 
permeable and the indigo-enzyme active. 
