348 SUBTERRANEAN ORGANS 



ness 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. 



Constituents. 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.) 



Uses. 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. 



Varieties. Many other plants furnish roots containing a similar 

 red colouring matter, e.g. Onosma echioides, Linne (S. Europe), 

 Macrotamia cephaldtes, de Candolle (Armenia and Syria), &c. ; they 



