Samples from a population of plants present in a grazed hill sward were isolated and grown as spaced individuals at a lowland site. The predominant taxa present were Agrostis, chiefly A. tenuis Sibth., and Festuca rubra L. Within each species, there was considerable variation between plants obtained from a relatively small area of sward. From an examination of morphological characters and tests of self- and cross-compatibility among plants, an indication of the number of genotypes present was obtained. Eighty-four putative genotypes of Agrostis and forty of Festuca were identified. A map is given showing the position of each putative genotype in the original population and the structure of Agrostis-Festuca swards is discussed.