Substance in Indigo-yielding Plants . 305 
roots, the root-stock, the cambium and secondary tissues of woad-roots, 
flower-buds, embryo, seeds, and fruits. 
Again, in 1900 ( 15 ), by the action of boiling hydrochloric acid and 
ferric chloride on a thin section, indigo will be found deposited in the 
epidermal cells, and especially the hairs, of young leaves. It is also 
precipitated in the mesophyll and other parenchymatous tissues. 
The sulphuric-acetic-persulphate reagent does not produce any large 
development of blue in Isatis, and it is consequently somewhat difficult 
to trace the locality of this deposition. In the epidermis precipitation 
occurs, especially in the guard-cells of the stomata. The main deposition 
occurs in the mesophyll and veins of the lamina, in which latter indigo 
occurs in all elements except the xylem-vessels. In the midrib there 
is only sufficient in the epidermis and extra-vascular parenchyma to give 
the faintest blue coloration. The merest traces occur in the parenchyma 
of the vascular strands of the midrib. The root-stock roots, flowering stalk, 
and organs of reproduction show no trace of blue after the above treatment. 
III. Polygonum tinctorium, Ait. 
As in the case of Isatis tinctoria , the present knowledge chiefly depends 
on the work of Molisch. According to him ( 5 ) the indigo-forming sub- 
stance can first be identified in the earliest foliage leaves, but not in the 
cotyledons ; in these latter none is present, nor is there any in the root or 
hypocotyl of the young plant. In the fully-developed plant all parts, 
except the leaf-lamina, are, after treatment, colourless and devoid of indigo 
blue. The petioles and principal veins of the leaf, the stipules, stem, root, 
flower, and fruit are therefore devoid of the indigoTorming substance. In 
the epidermal cells of the lamina there is little, nor is there any abundance 
of indigo deposited in the parenchyma of the vascular bundles. In the 
mesophyll alone is it deposited in any quantity. 
Beyond this little or no work has been undertaken on the localization 
in this plant. The examination made by Beijerinck in 1900 (10) is only 
of a cursory nature, and his results, as far as they are stated, agree with 
those of Molisch as given above. 
The present examination indicates that, as Molisch has shown, the 
leaf-lamina — especially of the young leaves — is the only locality where 
the dye-producing substance occurs. Beyond this, however, there is little 
agreement between the present results and those obtained by Molisch. 
The greatest deposition of indigo occurs in the epidermis, including both 
the guard-cells and the epidermal hairs. In the unspecialized epidermal 
cells deposition is so great that the plasma and nucleus are rarely dis- 
tinguishable. 
The mesophyll contains a considerable amount of indigo, and so 
