Mentha viridis is regarded by Bentham as not improbably a variety of M. silvestris L., perpetuated through its ready propagation by suckers. J. G. Baker remarks, that while these two plants are sufficiently distinct as found in England, yet continental forms occur which bridge over their differences.[1757]
History—Mint is mentioned in all early mediæval lists of plants, and was certainly cultivated in the convent gardens of the 9th century. Turner, who has been called “the father of English botany,” states in his Herball[1758] that the garden mint of his time was also called “Spere Mynte.” We find spearmint also described by Gerarde who terms it Mentha Romana vel Sarracenica, or Common Garden Mint, but his statement that the leaves are white, soft, and hairy does not well apply to the plant as now found in cultivation.
Description—Spearmint has a perennial rootstock which throws out long runners. Its stem 2 to 3 feet high is erect, when luxuriant branched below with short erecto-patent branches, firm, quadrangular, naked or slightly hairy beneath the nodes, often brightly tinged with purple. Leaves sessile or the lower slightly stalked, lanceolate or ovate-lanceolate, rounded or even cordate at the base, dark green and glabrous above, paler and prominently veined with green or purple beneath, rather thickly glandular, but either quite naked or hairy only on the midrib and principal veins, the point narrowed out and acute, the teeth sharp but neither very close nor deep, the lowest leaves measuring about 1 inch across by 3 or 4 inches long. Inflorescence a panicled arrangement of spikes, of which the main one is 3 or 4 inches long by ⅜ inch wide, the lowest whorls sometimes ½ an inch from each other and the lowest bracts leafy. Bracteoles linear-subulate, equalling or exceeding the expanded flowers, smooth or slightly ciliated. Pedicels about ¾ line long, purplish glandular, but never hairy. Calyx also often purplish, the tube campanulato-cylindrical, ⅜ line long, the teeth lanceolate-subulate, equalling the tube, the flower part of which is naked, but the teeth and often the upper part clothed more or less densely with erecto-patent hairs. Corolla reddish-purple, about twice as long as the calyx, naked both within and without. Not smooth.
The plant varies slightly in the shape of its leaves, elongation of spike and hairiness of calyx. The entire plant emits a most fragrant odour when rubbed, and has a pungent aromatic taste.
Production—Spearmint is grown in kitchen gardens, and more largely in market gardens. A few acres are under cultivation with it at Mitcham, chiefly for the sake of the herb, which is sold mostly in a dried state.
The cultivation of spearmint is carried on in the United States in precisely the same manner as that of peppermint, but on a much smaller scale. Mr. H. G. Hotchkiss of Lyons, Wayne County, State of New York, has informed us that his manufacture of the essential oil amounted in 1870 to 1162 lb. The plant he employs appears from the specimen with which he has favoured us, to be identical with the spearmint of English gardens, and is not the Curled Mint (Mentha crispa) of Germany.
Chemical Composition—Spearmint yields an essential oil (Oleum Menthæ viridis) in which reside the medicinal virtues of the plant. Kane,[1759] who examined it, gives its sp. gr. as 0·914, and its boiling point as 160° C. The oil yielded him a considerable amount of stearoptene. Gladstone[1760] found spearmint oil to contain a hydrocarbon almost identical with oil of turpentine in odour and other physical properties, mixed with an oxidized oil to which is due the peculiar smell of the plant. The latter oil boils at 225° C.; its sp. gr. is 0·951, and it was found to be isomeric with carvol, C₁₀H₁₄O. According to our experiments the oil, distilled from Curled Mint grown in Germany, deviates the plane of polarization 37°·4 to the left when examined in a column of 100 millimetres. We prepared from it the crystallized compound (C₁₀H₁₄0)₂SH₂, and isolated from it the liquid C₁₀H₁₄O, which differs from carvol (see Fructus Carui, page 306) by its levogyrate power.[1761]
Uses—Spearmint is used in the form of essential oil and distilled water, precisely in the same manner as peppermint In the United States the oil is also employed by confectioners and the manufacturers of perfumed soap.
Substitutes—Oil of spearmint is now rarely distilled in England, its high cost[1762] causing it to be nearly unsaleable. The cheaper foreign oil is offered in price-currents as of two kinds, namely American and German. Of the first we have already spoken: the second, termed in German Krauseminzöl, is the produce of Mentha aquatica L. var. γ crispa Bentham, a plant cultivated in Northern Germany. Its oil seems to agree with the oil of spearmint.