The possibility of using microscopic characteristics of the leaf epidermis as aids to the identification of some British agricultural grasses in the vegetative condition has been investigated.The occurrence of the following types of differentiated cells on the leaf‐sheath was markedly affected by the stage of growth of the tiller: silica cells, silico‐suberose couples, cork cells, asperities and incipient asperities. These cells were frequently absent or confined to the base of the sheath in vegetative tillers, but they occurred over most of the sheath in culm leaves. Silica cells tended to preponderate in young tillers and silico‐suberose couples and cork cells in the reproductive stage. The inter‐nerve epidermis of the leaf‐blade was generally the least affected by growth stage; although less differentiated than the sheath, it was found to be the most useful location for identification purposes. Species separable on the basis of the above‐mentioned characters of the leaf‐blade were:—(a)Tall fescue (Festuca arundinacea) from meadow fescue (F. pratensis)(b)Heath‐grass (Sieglingia decumbens) from smooth‐stalked meadow grass (Poa pratensis)(c)Sheep's fescue (F. ovina), from mat‐grass (Nardus stricta) wavy hair‐grass (Deschampsia flexuosa) and bristle‐leaved bent (Agrostis setacea).Timothy (Phleum pratense), meadow foxtail (Ahpecurus pratensis) and bent (Agrostisspp.) were separable on the following characteristics, which were not affected by growth stage: the occurrence of crystal clusters precipitated by hot water in timothy and occasionally in meadow foxtail, but not inAgrostisspecies, the peculiar shape of undifferentiated cells of the nerve epidermis inAgrostisspecies, and the dense cover of asperities on the ligules ofAgrostissp