Much of the work tha thas been performed on the effects of seed size and temperature has been carried out on annual species. The studies that have been made on tree species have mainly concentrated on those of ecological significance. Little attention has been paid to crop species and, for Prunus, no studies have examined the influence of seed size or temperature on plant growth. Around the world, the majority of stone fruit root stocks are produced from seed. Problems have been encountered by both nurserymen and growers with the quality and uniformity of budded trees produced from such seedlings. Therefore, in this study, we have assessed the influence of seed size and temperature on germination and seedling growth of five cultivars of peach and nectarine root stocks with varying chill requirements for bud break.