170 MEDICINAL AND POISONOUS PLANTS 
Volatile oils form the most important constituent of a 
number of non-poisonous drugs which we have already stud- 
ied in the last chapter as food-adjuncts; namely, lemon, 
caraway, anise, cardamoms, spearmint, sage, ginger, and 
Fic. 163.—Medicinal Rhubarb (Rheum officinale, Buckwheat Family, 
Polygonacee). Plant in flower. A, flower, entire, enlarged. B, same, 
cut vertically. C, pistil; d, nectar glands. (Baillon.)—Perennial 
herb growing ’2 m. tall; leaves hairy; flowers greenish; fruit, dry, red- 
dish. Native home, Central Asia. 
hops. The drugs calamus, asafetida, and saffron are the only 
others of this class which call for mention here. Calamus 
consists of the underground stem of the sweet-flag (Fig. 167). 
It contains about 1% of a volatile oil to which it owes 
