Peppermint
2 of the 6 encyclopedias on this shelf carry an entry for Peppermint. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a well known flavor obtained from a species of mint. This mint is cultivated for commercial purposes, in Japan, Saxony, England, New York , the southwestern corner of Michigan, and adjacent parts of northern Indiana. Reclaimed peat swamps are the best of soil for peppermint. The running root-stocks are cut into short pieces and dropped in drills like seeds. In early autumn the crop is cut and cured like hay. Weeds must be excluded or they will spoil the flavor of the peppermint. The essence is obtained by putting the plants through a process of distillation which, in brief, consists of boiling in a closed still. The volatile oil contained in minute oil cells, chiefly in the leaves, escapes through a pipe with the steam, and is caught and cooled. An acre of peppermint should yield from ten to forty pounds of oil. The price varies from 75 cents to $4 a pound according to season. Growers consider $2 a pound a good price. Oil of peppermint is used chiefly in candies and medicines. It is also a remedy for toothache. Certain lands about Niles, Michigan, were considered undesirable until some one discovered that the soil was peculiarly adapted to the growing of peppermint. Michigan leads in the production of peppermint, raising three-fifths of the entire world's product. There were produced in 1900 in that state 164,177 pounds of peppermint oil, quite enough to flavor a good share of the world's candy.
Collier's New Encyclopedia (1921)
Mentha piperita, a mint with oblong, lanceolate, serrate, glabrous leaves; pedicels and flowers nearly smooth; flowers in cylindrical spikes, interrupted below. Probably a garden form of M. aquatica. Oil of peppermint, the oil distilled from the fresh flowers of M. piperita.
What Has Changed in the Last Century
Aiton's boast of 1910 that Michigan raised "three-fifths of the entire world's product" no longer holds: verticillium wilt in the mid-20th century drove the crop out of the reclaimed peat swamps around Niles, and US peppermint growing shifted west to the Pacific Northwest, with Oregon, Washington and Idaho now leading. World supply of mint oil and menthol is dominated today by India, grown largely from a different species, the cornmint Mentha arvensis. Collier's 1921 guess that M. piperita is "probably a garden form of M. aquatica" was half right: it is a sterile hybrid of M. aquatica with spearmint, M. spicata, propagated by root cuttings just as Aiton's described. The old toothache remedy has a modern medical descendant in enteric-coated peppermint oil capsules prescribed for irritable bowel syndrome.
Written for this edition, 2026.