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
Linnæan 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.
I trust that the present note, through the medium of _The Garden_,
will prevent the perpetuation of this error. This is the more
important, as I hope that the plant will come into cultivation in this
country. It is a robust plant of rapid growth, as easily cultivated as
the English peppermint, and seems to require less moisture, and is
therefore capable of cultivation in a great variety of localities. The
increasing demand for menthol, which can only be procured in small
quantities from the English peppermint, and the high price of English
peppermint oil, lead to the hope that instead of importing menthol
from Japan, it will be prepared in this country from the Japanese
plant.
With the appliances of more advanced civilization, it ought to be
possible for the oil and menthol to be made in this country at less
price than the Japanese products now cost.
At the present time large quantities of cheap peppermint oil are
imported into this country from the United States, and Chinese oil is
imported into Bombay for use in the Government medical stores. There
is no reason why this should be the case if the Japanese plant were
cultivated in this country. In Ireland, where labor is cheap and the
climate moist, this crop might afford a valuable source of income to
enterprising cultivators. It may be interesting to note here that the
plant used in China closely resembles the Japanese one, differing
chiefly in the narrower and more glabrous leaves. I have therefore
named it Mentha arvensis f. glabrata, from specimens sent to me from
Hong Kong, by Mr. C. Ford, the director of the Botanic Gardens there.