180 MEDICINAL AND POISONOUS PLANTS 
from the circumstance that they are commonly associated 
in plants with volatile oils it is supposed that they are derived 
from the latter by oxidation; but they are often complex 
mixtures of obscure chemical composition. Comparatively 
few resins are poisonous, and of these, only those contained 
in the drugs called male-fern and Indian hemp need here 
Fic. 171, I—Indian Hemp (Cannabis sativa, Mulberry Family, Moracee). 
Staminate and pistillate plants. (Baillon.)—An annual 1-3 m. tall; 
leaves roughish; flowers greenish; fruit dry. Native home, Central 
Asia. 
concern us. It is the dried and pulverized underground stem 
of the male-fern (Fig. 170) and related species which con- 
stitutes the drug long known as a most valuable means of 
expelling tapeworms. The resin, which is the active con- — 
stituent, has proved, however, in overdoses to be a violent 
