SEED-BEARING PLANTS 
479 
421. Mint Family (Labiatae). The Mint family is 
characterized by a square stem, opposite leaves, a tubular 
calyx, caused by the coalescence of the five sepals, a highly 
modified corolla having two lips or labia (singular labium, 
whence the family name), and leaves containing many 
FIG. 363. Bindweed (Convolvulus arvensis). 
small glands that secrete a volatile oil, which gives the char- 
acteristic odor and taste to all the plants of the family. 
The upper lip results from the fusion of two petals, the 
lower lip by the fusion of three. Everyone is familiar 
with one or more of these features, as embodied in the 
various mints, pennyroyal, horehound, catnip, sage, 
savory, thyme, hyssop, wild marjoram, and other condi- 
