RHIZOMES. 117 



bium layer is very distinct, three to five cells in width. 

 Within it is the central cylinder, made up of radial rows 

 of parench>Tna with some larger, comparatively thick- 

 walled, pitted reticulate, and spirally thickened ducts, 

 single and in groups of two and three. The cells of the par- 

 enchyma are filled with a yellow substance soluble in 

 water. Occasionally an oil globule or a sac of calcium 

 oxalate is seen, but neither starch nor tannin is present. 

 In no portion of the root are either bast or wood fibres 

 discernible. 



The Powder. — Owing to the absence of particularly 

 characteristic tissue the powder is identified only with 

 difficulty. The collenchymatic tissue lying within the 

 cork is of some value, also the large spiral and reticulate 

 ducts, and the regularity in both size and arrangement 

 of the cells next within the cambium. The absence of 

 bast fibres is of noteworthy importance. 



Chemistry. — The bitter principle is gentio-picrin, a 

 glycoside, crystallizable in colorless needles. It is readily 

 soluble in water and alcohol, split up by boiling with weak 

 acids into a fermentable sugar and glutio-genin. The 

 coloring-matter is gentisin (gentianin or gentisic acid) in 

 yellow tasteless crystals of neutral reaction, scarcely 

 soluble in water, more so in alcohol and ether, yielding a 

 brown color with ferric salts. A sugar, gentianose, is 

 found in the fresh root; it is fermentable but does not 

 reduce Fehling's solution. Fat, oil, resin, mucilage, 

 pectin, and 8 to 9 per cent, of ash are also present. 



RHIZOMES. 



Rhizomes are underground stems and are to be dis- 

 tinguished from roots by the presence of leaves or leaf 

 traces. Rhizomes may be horizontal, oblique, or vertical, 

 and can be distinguished by the situation of the leaf 

 scars or traces of the roots. In horizontal rhizomes the 



