Susan G. Letcher
Department of Biology, Carleton College, Northfield, MN, USA, 55057
Abstract. Selective seed abortion, which can be attributed to several factors, produces species-specific patterns of seed set. The pattern and amount of seed set in plants are often affected by environmental variables such as nutrient availability. I examined fallen pods of Pentaclethra macroloba on three soil types (swamp, alluvial, and residual) in order to examine environmental effects on the pattern and amount of seed set. There was a significantly non-random distribution of mature seeds in the pod, with very few mature seeds in the proximal end. In addition, soil type had a significant effect on the number of chambers per pod and the number of mature seeds per pod. Both these variables were highest in the swamp, and lowest on residual soils. The pattern of seed set provides support for several theories concerning selective seed abortion in legumes, and the effect of soil type on reproductive success supports the idea of a "rescue effect" (sensu Stevens 1989).