Summary:Plants of wild myrtle (Myrtus communisL.) collected at full bloom contained substances inhibitory to the germination and seedling growth of perennial ryegrass. (Lolium perenneL. cv Hollandi)Tissue suspensions had a greater inhibitory activity than water extracts of the plant tissue. Boiling the plant material also increased the inhibitory activity of suspensions and extracts. Flower, and buds, fruit covers and leaves had the greatest inhibitory effect/unit weight ot tissue but inhibitory activity was also present in stems and roots at lower concentrations.The effect of myrtle leaf suspensions on germination of seed of thirteen common garden flowers was also examined: Germination ofPetunia. Antirrhinum, Liaum. CheiranthusandLathyruswas inhibited completely or substantially depressed. Germination ofZinnia, Tagrtes. VerbenaandDianthuswas not much affected, while that ofBrllis. Gaillardia. andViolawas affected to an intermediate extent.These results suggest that the possible use of wild myrtle as an evergreen hedge plant needs to be examined further because of possible interference with the growth of nearby lawns and flowers.