PEPPERMINT 569 



slightly pubescent on the veins, glandular-pubescent; petiole 4 to 10 

 mm. in length, slightly pubescent. Inflorescence in axillary whorls 

 or in compact spikes; peduncle wanting or about 3 mm. in length, 

 pedicel about 1 mm. in length; calyx tubular, equally 5-toothed, 

 about 2 mm. in length, purplish, glandular-punctate; corolla tubular, 

 nearly regular, 4-cleft, about 3 mm. in length, purplish; stamens 

 four, erect, distant. Nutlets ellipsoidal, about 0.4 mm. in diameter, 

 blackish-brown. Odor aromatic; taste aromatic, followed by a 

 cooling sensation. 



INNER STRUCTURE. (Fig. 240). 



Crystals of menthol may be observed in the glandular hairs of 

 Mentha piperita, if the sections are kept at a temperature near 

 C., or by placing the sections in a freshly preserved solution of 

 ammonium nitrate (50 per cent.). The crystals separate in aggre- 

 gates consisting of small needles. Photomicrographs of menthol in 

 form of small rods and aggregates of needles are illustrated in Krae- 

 mer's Applied and Economic Botany, p. 326. 



Powder. Dark green; non-glandular hairs 1- to 8-celled, thin- 

 walled, with numerous papillose projections; glandular hairs two 

 kinds, 1- or 3-celled stalk and 1- or 8-celled glandular head; pollen 

 grains somewhat spheroidal, smooth, about 0.035 mm. in diameter; 

 tracheae spiral, or with simple and bordered pores, and slightly lig- 

 nified; sclerenchymatous fibers thin-walled, non-lignified, with 

 numerous oblique pores. Contamination with M. spicata is said to 

 be common. 



Constituents. Volatile oil, containing 50 to 60 per cent of men- 

 thol, about 1 per cent; resin and tannin. American peppermint oil 

 consists of about 17 different chemical constituents, a larger number 

 than is found in any other oil. The most important constituent is 

 the stearoptene menthol, of which 40 to 45 per cent is free and 8 to 14 

 per cent is combined in various esters. Menthol occurs in colorless, 

 acicular crystals, which are insoluble in water but soluble in alcohol, 

 and on boiling with a sulphuric acid solution (50 per cent) it becomes 

 of a deep blue color, the acid solution becoming brown. American 

 peppermint oil also contains: Acetaldehyde, isovaleraldehyde, acetic 

 acid, valerianic acid, pinene, phellandrene, cineol, 1-limonene, men- 

 thone, menthyl acetate, menthyl iso-valerianate, menthyl ester, a 

 lactone cadinene, amyl alcohol, and dimethyl sulphide. 



ENGLISH PEPPERMINT oil is very highly prized on account of 

 its fine aroma and pleasant taste. It consists of 50 to 60 per cent 

 of free menthol, 3 to 14 per cent of menthol combined as esters, 

 and 9 to 12 per cent of menthole, a substance capable of being trans- 



