This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Alkanet root is obtained from Alkanna tinctoria, Tauscher (N.O. Boragineoe), a small herbaceous plant with perennial root growing in sandy soil in southern Europe, Hungary, and Asiatic Turkey, our supplies being derived chiefly from Hungary.
The drug consists of deep reddish purple, simple, tapering roots averaging about 15 cm. in length, and 12 mm. in thickness near the crown, to which slender branches and the remains of leaves are attached; the latter have a purplish colour, and bear numerous, bristly hairs.
The root has a very remarkable appearance. The outer layers, which are deeply coloured, easily exfoliate, separating from the wood in large, papery flakes or strips; these are readily removed, and the exterior of the root is then the inner layers of cortical tissue. It is not smooth but more or less deeply furrowed longitudinally, the furrows being often so deep as to divide the wood into separate woody strands. Cut transversely in the upper part the root exhibits a dark violet spot in the centre, and a woody ring containing several radiating strands of dense woody tissue separated by large wedge-shaped masses of parenchyma; the bark is yellowish near the wood, but becomes coloured and laminated towards the exterior. From near the crown of the root downwards the violet spot in the centre becomes larger and the colouring matter in the bark penetrates deeper until by their union the separation of the strands of wood is complete.
The root when handled stains the fingers red. It has no perceptible odour or taste.
The students should observe
(a) The dark reddish purple colour of the parenchymatous tissue and whitish colour of the wood,
(b) The hairy remains of the leaves.
Alkanet root is said to contain two red colouring substances, viz. anchusic and alkannic acids, the former turning green with alkalies and the latter blue. Alkannin is the name given to an oleo-resinous mixture of deep red colour obtained by extracting the root with petroleum spirit or benzene and evaporating. These substances are produced first in the epidermal cells and hairs of the young roots. After the cortical parenchyma has been thrown off some of the parenchymatous cells within the pericycle rupture, and in the intact cells next to the ruptured ones the formation of the colouring matter proceeds rapidly; cork cells form a little deeper in the tissue, resulting in the formation and rejection of a succession of deep red scales which extends to the wedges of parenchyma that divide the wood into strands; these perish, and thus the remarkable appearance of the commercial drug is explained. (Ericksson, 1910).
Alkanet is used for colouring oils, ointments, &c; the tincture, diluted with an equal volume of water, is used for the microscopical detection of fat and oil, which it colours red.
Many other plants furnish roots containing a similar red colouring matter, e.g. Onosma echioides, Linne (S. Europe), Macrotamia cephalotes, de Candolle (Armenia and Syria), etc.; they are occasionally substituted for the root of Alkanna tinctoria, the Syrian drug being apparently more than half as rich again in colouring matter as the Hungarian. Both of these substitutes are larger than alkanet root.