Adelaide, S.A., April, 1883.
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In more than one periodical the botanical name of this plant has been given as Mentha arvensis, var. purpurascens. It will be well, therefore, to point out that this is an error before the statement is further copied and the mistake perpetuated. The plant has green foliage, with not a trace of purple, and less deserves the name purpurascens than the true peppermint (Mentha piperita), of which a purplish leaved form is well known. The mistake probably arose in the first place in a printer’s error. The history is as follows:
For some years past a large quantity of a substance called menthol has been imported into this country, and extensively used as a topical application for the relief of neuralgia, and in some instances as an antiseptic. This substance in appearance closely resembles Epsom salts, and consists of crystals deposited in the oil of peppermint distilled from the Japanese peppermint plant. This oil, when separated from the crystals, is now largely used to flavor cheap peppermint lozenges, being less expensive than the English oil. The crystals deposit naturally in the oil upon keeping, but the Japanese extract the whole of it by submitting the oil several times in succession to a low temperature, when all the menthol crystallizes out from the oil and falls to the bottom of the vessel. The source of the Japanese peppermint oil has been stated to be Mentha arvensis, var. javanica. On examining several specimens of this plant in our national herbaria I found that the leaves tasted like those of the common garden mint (Mentha viridis), and not at all like peppermint, and that therefore the oil and menthol could not possibly be derived from this plant.
I then asked my friend, Mr. T. Christy, who takes great interest in medicinal plants, to endeavor to get specimens from Japan of the plant yielding the oil. After many vain attempts, he at last succeeded in obtaining live plants. These were cultivated in his garden at Malvern House, Sydenham, and when they flowered I examined the plant and found that it differed from other forms of M. arvensis in the taste, in the acuminate segments of the calyx of the flower, and in the longer leaf stalks; the leaves also taper more toward the base. Dr. Franchet, the greatest living authority on Japanese plants, to whom I sent specimens, confirmed my opinion as to the variety deserving a special name, and M. Malinvaud, a well known authority on mints, suggested the name piperascens, which I adopted, calling the plant Mentha arvensis, var. piperascens. Specimens of the plant kindly lent by Mr. Christy for the purpose were exhibited by me at an evening meeting of the Linnaean Society, and by a printer’s error in the report of the remarks then made, the name of the plant appeared in print as Mentha arvensis, var. purpurascens.