Résumé
Using a combination of observations of fate of ovules in matured fruits and of fluorescence techniques to study pollen tube growth and fertilization of ovules, we examined patterns of seed formation within pods in natural populations of two species of Lathyrus, L. sylvestris and L. latifolius. We also examined variation in these patterns within and among populations and between two consecutive years. In both species, only a portion of the ovules were fertilized. Fertilization occurs over a period of several days and ovules at the stigmatic end of the fruit are the first to be fertilized. Fertilized ovules farthest from the stigma are closest to the maternal nutrition. The pattern of embryo abortion is interpreted as a balance between the early start and genetic quality of embryos near the stigma, on the one hand, and the nutritional advantage of proximity to maternal nutrients, on the other. Differences between the two species in patterns of seed maturation are postulated to be related to differences in breeding system. In L. sylvestris , a higher frequency of selling leads to less genetic diversity of pollen deposited on the stigma, lower competition among potential sires, and a more nearly random pattern of ovule fertilization and maturation within the pod.