This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This British and European perennial is now cultivated extensively both in the open air and under glass by many market gardeners, and has been dealt with specially at p. 116. Peppermint (M. piperita), so much used for the preparation of the cordial bearing its name, may be grown in the same way as the ordinary Mint, in any good garden soil. Pennyroyal (M. Pulegium) emits a powerful aromatic odour, and is used medicinally. It likes strong loamy soil, and is increased by division.