Young apple trees were grown in Bristol, England for 1 yr until Jan. 1975, when half the batch was moved to Montpellier in the south of France; in Jan. 1976, 6 trees were returned to Bristol and a further 6 sent to Montpellier. From early 1975 until the end of 1976, flowering and growth patterns were monitored and measurements of dry matter production were made at both sites. Continuous weather measurements were also made. Over the growing period in 1975, Montpellier received 18% more radiant energy than Bristol; in 1976 it received 24% more. Spring temperatures were higher and dew points generally lower at Montpellier than Bristol. Full bloom was reached about mid-April in France and early to mid-May in England. Fruit number per flower cluster was 2-3 times higher in England than in France. Shoot growth started about 3 wk earlier in France and leaf area per tree was always higher there. Up to the time of crop harvest in 1975, dry matter production by the trees in England, which had more fruits than the trees in France, was greater than in France but, over the whole season, dry matter production was 12% greater in France. In 1976, fruit loads were approximately the same at the 2 sites, and differences in dry matter production were proportional to leaf area duration and total radiant energy received; dry matter production in France was greater than in England up to crop harvest and 25% greater overall. Fruit number per unit area was the main determinant of the partitioning of assimilates.