( 510) 
space shut off from the air, and that the yellowish red solution has 
acquired the property of turning blue even without being heated. 
In the formation of dipsacotin from dipsacan a chemical transformation, 
which can only occur on warming, evidently takes place first; the 
subsequent oxidation can also proceed at the ordinary temperature, 
although it is greatly accelerated by warming. 
Of the properties of dipsacotin I only propose to mention, that 
this colouring matter is soluble in water, that it is decomposed by 
sulphuric acid with the formation of a yellowish red product, and 
that it is decomposed by light; three points in which it differs from 
indigo. 
The chromogen dipsacan is decomposed by acids and by alkalies, 
and can only exist in a feebly acid solution, such as that of the 
extract. Acids and alkalies do not, however, ever on heating, produce 
the transformation-product which by oxidation forms dipsacotin. 
This is formed from dipsacan, not only by warming above 35°C., 
but also at the ordinary temperature, through the agency of dipsacase, 
the enzyme occurring in the plant. This perhaps explains an observation 
made long ago by pr Vries *), that the press-juice of Dipsacus 
fullonum becomes black after a few days’ exposure to the air. 
Probably the juice contains both the chromogen and the enzyme, 
and the former is decomposed by the latter. That the colour, after 
oxidation, is black and not blue, may perhaps be attributed to the 
presence of other substances, or to other chemical reactions taking 
place simultaneously. 
Dipsacan occurs in all organs, even including the flower and the 
seed, and all tissues, except the pith of the stem, contain it. The 
cellwall is probably free from dipsacan, as it does not become 
coloured blue. 
The quantity of the chromogen, present in the various organs, 
depends on internal and external causes. Young parts growing 
vigorously, contain most. Under favourable conditions of life the 
quantity is larger than under unfavourable; af temperatures which 
approach the limits of life of the plant, the quantity of dipsacan is 
less. Light exercises no direct influence on the presence of the chromogen. 
In the dark the dipsacan does not disappear from the leaves, but it is 
formed in new, completely etiolated ones. Dipsacan is therefore not 
directly related to carbon-assimilation. More probably the chromogen 
takes part in metabolism, and as it occurs in the plant in such large 
1) Hueco pe Vries, Een middel tegen het bruin worden van plantendeelen by het 
vervaardigen van praeparaten op spiritus. Maandbl. v. Naluurw. 1886, No. 1. 
