630 BOTANY AND PHARMACOGNOSY. 



remotely serrate; upper surface dark green, pubescent on the 

 nerves, slightly glandular-hairy ; under surface light green, pubes- 

 cent, glandular-hairy, veins of the first order diverging at an angle 

 of 45° to 65", curving upwards and uniting near the margin; 

 petiole 3 to 6 mm. longl'-^ with numerous spreading hairs and 

 slightly laminate in the upper portion. Inflorescence in six- 

 flowered axillary whorls ; calyx tubular, about 5 mm. long, ovoid 

 or slightly curved on the lower side near the base, bilabiate, upper 

 lip 3-toothed, lower lip with two linear-lanceolate divisions, 13- 

 nerved, longitudinally striate, pubescent ; corolla about the size 

 of the calyx, purplish, pubescent, upper lip erect, flat, emarginate, 

 the lower spreading and 3-lobed; fertile stamens two, exserted, 

 ascending, the sterile upper pair rarely with anthers. Nutlets 

 nearly spherical or ovoid, about 0.5 mm. in diameter. Odor 

 strongly aromatic. Taste aromatic. 



Constituents. — Volatile oil, a bitter principle and tannin. 

 The dried leaves yield about 3 per cent, of volatile oil, while the 

 dried stems and leaves yield only 1.3 per cent. The volatile oil 

 is official and consists chiefly .of a ketone pulegone, which gives 

 the oil its peculiar properties. 'The oil also probably contains 

 two other ketones: (a) hedeomol and (b) another resembling 

 menthone. Several acids have also been found in this oil : formic, 

 acetic and isoheptylic. 



Allied Plants. — Mentha Pulegium, or European pennyroyal, 

 apparently contains principles similar to the American penny- 

 royal, and is distinguished from the latter by the more or less oval, 

 serrate leaves, and the cymose inflorescence and four-lobed corolla. 

 The oil of European pennyroyal closely resembles that of Hede- 

 oma and is frequently substituted for it. 



Wild Mint {Mentha canadensis) , a perennial herb common 

 in wet places in the United States, has ovate-oblong or lanceolate 

 leaves, in the axils of which whorls or globular clusters of flowers 

 arise. The plant has an odor of pennyroyal and yields 1.25 per 

 cent, of a volatile oil from which pulegone and thymol or carvacrol 

 have been isolated. 



Water Mint {Mentha aquatica), a plant found in wet places 

 from New England to Delaware, yields about 0.34 per cent, of a 

 volatile oil having the odor of pennyroyal. 



