22 



THE SOURCE OF THE DRUG DIOSCOEEA. 



mata, it being very difficult to powder or crush. It has no odor and but liUIe 

 taste beyond a slight acridity after prolonged chewing. The virtues appear to 

 reside in an acrid resin, almost insoluble in water, but readily extracted by 

 alcohol. The so-called dioscorein is not a definite principle of the rhizoma, but 

 is simply a dried solid extract, and to call it otherwise is a misnomer. 



Dioscorea villosa var. gJahra. — This appears to us to be a distinct variety, 

 chiefly differing from the preceding in the entire dissimilarity of its rhizomata. 



This plant closely resem- 

 bles the true wild yam 

 in its general shape, and 

 in the structure of its 

 leaves, flowers, and fruit. 

 The leaves, however, are 

 entirely glabrous and are 

 not covered with a short 

 pubescence underneath. 

 This distinction we have 

 invariably found in every 

 instance where we have 

 examined the growing 

 plants, hence the under- 

 surface of the leaf will 

 readily determine the 

 character of the rhizoma. 

 The two plants likewise 

 appear to differ in their 

 manner of growth, the 

 D. villosa often growing 

 in dense clumps while 

 the variety ylahra is gen- 

 erally found isolated. 



The rhizoma (PI. VII, 

 fig. 1) of I>, villosa var. 

 glabra i-esembles that of 

 Colliiisonia Canadensis 

 more nearly than it does 

 the true D. villosa. It is 

 found as a rough clump 

 of a pound or more in 

 weight when fresh, 

 thickly branched, each 

 branch shooting from the 

 side of the main rhizoma 

 at an angle inclining 

 backward and upward. 

 The branches almost 

 touch each other, are as 

 large as the rhizoma, and 

 are from 1 inch to 3 inches in length. Along their upper surface are numerous 

 cup-shaped stem scars, which are about one-fourth of an inch or one-third of an 

 inch in diameter and so thickly inserted as to intrude upon each other. The 

 vine of the true D. villosa, upon the contrary, springs fi'om the main rhizoma. 

 The diameter of the rhizoma and of the ramifications is from half an inch to 

 three-fourths of an inch, and the length seldom mox'e than 6 inches. Internally 

 189 



Fig. 5. — Rhizome of Dioscorea glaucu. Mountain form 

 from the summit of House and Barn Mountain in Russell 

 County, Virginia, collected by C. L. Alsberg. (Three- 

 fourths natural size.) 



