230 DK. EDWARD SCHUNCK ON INDIGO-BLUE. 



This red colour disappears on immersion of tlie leaves in • 

 hot alcohol, the indirubine, to which it is probably due, 

 being more soluble in that menstruum than indigo-blue. 



The leaves of Polygommi tinctorium in which the blue 

 colour has been developed by any of the means described, 

 exhibit even to the naked, eye, and still more distinctly 

 when examined under the microscope, certain appearances 

 which are not without some interest. 



1. The colouring-matter seems to be confined to the 

 parenchyma of the leaf. The stem and its fibrous rami- 

 fications in the leaf are free from it, so that in the coloured 

 leaf the vessels may be distinctly traced as Avhite veins on 

 a blue ground. Even the cells of the parenchyma adjacent 

 to the vessels are much less coloured than those a little 

 further off, which produces the effect of a gradual shading 

 of colour from the white of the vessels to the dark blue of 

 the remoter cells. The cells of the leaf-cuticle are also 

 free from colouring-matter. 



2. The younger leaves at the summit of each branch 

 generally show a more intense colour than the older ones 

 near the base. Each leaf probably contains the same 

 amount of colouring-matter ; but in the lower leaves it is 

 more widely distributed. 



3. The intense and apparently uniform coloration of 

 some of the leaves might lead to the conclusion that the 

 cellular tissue is itself dyed blue — which would not seem 

 improbable, considering the affinity which indigo-blue 

 shows for cellulose, as seen in the blue dyeing of cotton 

 fabrics. On examining the leaf-cells under the microscope, 

 this is found, however, not to be the case. The colouring- 

 matter is discovered within the cells of the parenchyma in 

 the shape of separate dots and parcels of various sizes, and 

 apparently in an amorphous state, the cell-wall being quite 

 colourless. These dots and parcels being very numerous. 



