335 



some hydrucliloric aoiil. K\ en nld ! iuiifiofcni-\ea.\es, which by the )>alcohol-cxperi- 

 nient« become quite colourless, takt- a l>rillant blue colour by this »nierriirv-ammoniac 

 experiment «. 



Before I had worked out the niercury-niethod, l exainintd the results of killinjj 

 the leaves by the asphixion in hydrogen, carbonic acid and the vacuüm, in each case 

 foliowed, in the same manner as in the mercury-niethod, by subsequent (.-xposition to 

 aminoniac-vapour and extraction of the chlorophyll with alcohol. 



When the hydrogen was mixed with air a singular phenomenon was observed : the 

 indoxyl disappeared so completely from the leaves, that, after the said treatment, 

 they became quite colourless, whilst pure hydrogen produced intensely blue leaves. 



In the carbonic-acid atmosphere there appeared, with the indigo, a small quan- 

 tity of brown pigment, probably because the carbonic acid was not wholly frec froni 

 air. The action of pure carbonic acid I have not vet examined. 



The vacuüm in a barometer-tube, above mercury, gives the same result as tlie 

 submersion in mercury itself, but this method is, of course, more complicated. 



3. Oh the iculoured stript, in partly killed leai'es. 



The foUowing phenomenon is in near relation to the preceding. In many leaves, 

 when partly dying off, a coloured matter will appear, just on the border between the 

 living and the dead tissue; with woad and with Polygoninn tinctoriunt. the chromo- 

 gene of this coloured strip is indigo '). The experiment succeeds best if the leaf is 

 partly killed by keeping it for a moment in the vapour of boiling water. The killed 

 part remains green, although it may be a little more brownish than the living oiie. 



As for woad I think the phenomenon should be explained as follows. 

 On the border between the dead and the living tissue, a strip af cells must occur 

 which are in a condition of slowly dying. According to the preceding description, 

 alkali will be fornied in these cells and the indoxyl quickly oxidises to indigo-blue, 

 nothing of it finding time for disappearing in another way. If the partly killed woad- 

 leaf, immediately after death sets in, is exposed to ammoniac-vapour, it becomes, as 

 might be expected, over its whole extent deeply blue. If it is, before the action of 

 the ammoniac, left for some time to the influence of the air, then some indoxyl gets 

 lost from the killed part which colours with ammoniac, a little less strongly than what 

 remained living. 



For PolyguHKiii tinctvriuiii the explanation is somewhat different, because the 

 indoxyl must first be originated by the action of the indigo-enzyme. But this enzymc 

 is destroyed by the hot vapour in the quickly dying part. whilst on the border be- 

 tween the living and the dead part there must be a number of cells in which the proto- 

 plasm is killed or hurt, but in w4iich the enzyme remains active. During the dying 

 the protoplasm becomes permeable, indican and enzyme are mixed up, and indoxyl- 

 formation is the result. But in the same cells there occurs, in consequence of the 



') With woad this experiment succeeds best with leaves from the rosettcs of the 

 first year in June; with Polygonum always equally'wcll. In many otlier plants the 

 ncoloured strip« does not contain indigo but a black or a brown pigment. 



