Experiments were concerned with the growth and development of flowers of carnation (Dianthus) var. White Sim from the time the flower buds became visible up to anthesis. Rates of growth in size of the flower were decreased by either low temperatures or low light intensities but only low temperatures caused an appreciable delay in anthesis. Effects of low light intensity could be simulated by partial defoliation and appeared to be mediated through effects on photosynthesis. Temperature, however, acted directly on processes occurring in the flower bud. The rate of development of the flower, in the sense of progress towards anthesis, appeared to be independent of levels of assimilates available for growth. It is suggested that processes controlling development in the flower regulate the partition of assimilates between the flower and the remainder of the shoot system. Seasonal variations in rates of flower development under glasshouse conditions are considered to be largely attributable to variations in the temperature of the flower buds.