umbelliferone residue) in preference to the alternative one with the heterocyclic oxygen located on C-6 of the coumarin residue. The mass spectrum exhibited fragmentations which are in agreement with structure II for ammirin, including M + (m/e 228) and ions at m/e 2t3, 200, 187, and t75 resulting from M+ by expulsions of CHa, CO, Calla, and C~Hs, respectively. Final proof of the structure was obtained by preparation of ammirin through controlled dehydration of marmesin (I) using phosphorus pentachloride in ether at room temperature. There is evidence to show tha t ammirin results partly from a parent glycoside (in which the sugar residue engages the phenolic hydroxyl group of the corresponding open coumarinic acid) and partly as an artefact from acid-induced dehydration of marmesin (1). Details of this study and further data wilt be published at a later date.