The description 'low mineral requirement' has often been applied to a species which has been found to grow satisfactorily on a medium with low concentrations of certain nutrients, upon which another species shows poor growth. While it may be correct to assume that the first species has a lower mineral requirement, the possibility also exists that it is able to exploit the resources of the medium more efficiently, thus satisfying similar requirements from a more restricted source of supply. If, in studies of this type, uptake of nutrients by the plant is considered in conjunction with data on growth responses it may be possible to determine whether one or both of these factors is in operation. The growth responses of calcicole and calcifuge plants to the calcium concentration in the external medium have been shown to differ in experimental studies by Olsen (1942), Bradshaw, Lodge, Jowett & Chadwick (1958) and Jefferies & Willis (1964). Direct comparisons are most easily interpreted where closely related species have been examined. In recent publications by Bradshaw et al. (1958), Snaydon & Bradshaw (1961) and Clymo (1962), related calcicole and calcifuge species were shown to respond to calcium levels in a manner which was closely correlated with the calcium status of the soil in which they normally grew. Olsen (1942), Snaydon & Bradshaw (1961) and Jefferies & Willis (1964) are amongst the few workers who have considered data on both calcium uptake and growth responses when arriving at conclusions concerning the calcium requirements of the species they examined. In sand culture experiments Bradshaw et al. (1958) determined the optimum calcium concentrations for the growth of Agrostis canina, A. stolonifera and A. tenuis. These levels were closely related to the calcium status of the soils in which the species are distributed. In the present work a comparison has been made of the calcium uptake and the growth responses of A. canina, A. setacea, A. stolonifera and A. tenuis to various calcium concentrations. Particular attention has been given to determining whether the wellmarked calcifuge species, A. setacea, grows satisfactorily with low internal concentrations of calcium or whether it is able to take up calcium from soil and water cultures more efficiently than the more mesic and calcicole members of the genus.