The oil of common-cress was first prepared by F. Pless'2) in 1846. He observed that the herb and seeds of Lepidium ruderale, L., also the seeds of Lepidium sativum, L. and Lepidium campestre, R. Br. (family Cruciferae) upon distillation yield sulphur-containing oils which sink in water. He assumed that the oil occurred as such in the herb, but that from the seeds it resulted upon the action of the water. According to whether the herb is comminuted or not, totally different oils are obtained.
A. W. Hofmann3) conducted the first scientific examination of the oil. He distilled the non-comminuted herb of Lepidium sativum, L. (Ger. Gartenkresse) immediately after the flowering period in a wooden still4) with water vapor. As the oil remained l) Comp. the chapter Die Senfdle in F. Czapek, Biochemie der Pflanzen, Jena 1905, vol. II., p. 232. - H. ter Meulen, Recueil trav. chim. des P.-B. 19 (1900), 33 and 24 (1905), 444. - A. Oliva, Vergleichende anatomische und entwicklungsgeschichtliche Untersuchungen uber die Cruciferensamen. Zeitschr. d. allg. osterr. Apoth. Ver. 43 (1905), 1001, 1033, 1073, 1109, 1141, 1169, 1197, 1225, 1253, 1281, 1309, 1343.
2) Liebig's Annalen ft (1846), 39.
3) Berl. Berichte 7 (1874), 1293.
*) Copper vessels should be avoided for the distillation of this and other sulphur-containing oils, otherwise a partial decomposition with the formation of copper sulphide takes place.
The fact that the herb of the garden-cress produces a prp-nounced odor of mustard oil, suggests to J. Gadamer1) that in all probability the investigation of A. W. Hofmann does not at all refer to the real oil of cress but to a decomposition product thereof, as has been observed in connection with the oil of Tropaeolum majus. Unless the herb is very carefully comminuted before distillation, the enzyme which it contains cannot reach the glucoside deposited in other cells, but is destroyed by the heat. Hence the hydrolysis of the glucoside into benzyl mustard oil and glucose cannot take place, but the direct action of hot water on the glucoside causes benzylcyanide, found by Hofmann, to be formed2).
The seeds of the garden-cress presumably contain the same substance which causes the formation of oil in the herb. If the ground seeds are subjected to the action of water1) and some white mustard seed for several hours and then distilled with steam, the distillate separates a slightly yellow-colored oil, the odor of which cannot be distinguished from that of the garden nasturtium (Tropaeolum majus). When treated with alcoholic l) Arch, der Pharm. 237 (1899), 508.
2) H. ter Meulen (Recueil trav. chim. des P.-B. 19 , 42) is of opinion that the abnormal results obtained by A. W. Hofmann were not due to imperfect comminution, as assumed by Gadamer, but to the large amount of material used for a single distillation. However, the distillation of a larger amount of material need not require more time than that of a small amount, provided the size of the still and the supply of steam be adequate. But if the material is not comminuted, the distillation lasts much longer. Consequently both expressions of opinion are in practical agreement as to results.
ammonia, crystals of benzyl thiourea, melting at 162°, separate. Hence the oil from the seeds of the garden-cress consists in part of benzyl mustard oil which owes its formation to a glucoside called glucotropseolin1), the latter being hydrolyzed by the enzyme myrosin contained in the white mustard oil. On account of its feeble capacity to crystallize the glucotropzeolin from the seed of the garden-cress has not been isolated thus far.
Upon distillation, the fresh herb of Lepidium latifolium, L.2) yields a sulphur-containing oil that sinks in water.