Obtained from crushed onion seeds, the seeds of Allium cepa L., Liliaceae: Loew, Ind. Quim. 10, 5 (1948); Phadnis et al., J. Univ. Bombay 17A, no. 24, 62 (1948). Contains allylpropyl bisulfide, S-(1-propenyl)cysteine sulfoxide and 1-propenylsulfenic acid which is thought to be the lacrimator in onions: Virtanen, Sprare, Suom. Kemistil. B 35, 28, 29 (1962); Chem. Ztg. 86, 816 (1962).