In the common milkweed, inflorescence size above a certain size is not correlated with seed set or pollination rates. The number of pods matured by each inflorescence is limited, and a minimum number of flowers appear to be necessary to ensure that pod production, within this limit, is maximized. Inflorescences larger than this optimum size for pod production may have particular selective value in contributing pollinia to other plants. The balance between the high-cost (per fruit), low-risk strategy of producing small inflorescences for pod production and the low-cost (per set of pollinia), high-risk strategy of large inflorescences for increasing pollinia production is probably adaptive. The partitioning of flowers among separate inflorescences permits an increase of pod production and may provide advantages from the temporal dispersion of blooming. INTRODUCTION Insect-pollinated plants have a great variety of evolutionary choices in the design of their floral displays. The flowers on a stem may be clustered in space and/or time, and flowering stalks may themselves be clumped in various ways and densities. The success of any floral display must be measured in terms of the number of viable offspring produced, which is likely to be a function of success in attracting effective pollinators and, perhaps, dispersers, and the avoidance of predators (Yeo, 1972). Burtt (1961) began to explore some of these relationships for Compositae, but little other work has been published on the evolution of floral arrangements. However, the general problem of the evolution of flowering strategies is attracting growing attention (e.g., Beattie et at., 1973; Heinrich and Raven, 1972; Janzen, 1971; Stebbins, 1970, 1971; Willson, 1972, 1973). The success of various flower arrangements, measured in terms of pollination and seed set, was examined as a function of clustering of flowers, pollination rates and predation. METHODS A. syriaca has small pinkish flowers displayed in simple, compact, many-lowered umbels, often several on each flowering stalk, and the fruit pods may-contains hundreds of seeds. Over 60 milkweed plants were sampled beginning in late June at the commencement of blooming.