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Coumarin and phytol were the stand-outs, Dr Cantrell said.

The second key ingredient he and his colleagues identified in sweetgrass was phytol, a common constituent in essential oils from plants.

Phytol, similarly, is known to repel insects but is not currently marketed for that purpose.

Phytol.—This alcohol, which furnishes the characteristic ester group in the chlorophyll of plants, is a compound of very unusual composition, which has never been found in any other form or in any other type of compound which is present in either plant or animal tissues.