Two experiments were conducted to determine the contribution of leaves at different stem positions to photosynthesis of peanut plants, and the change in this contribution with plant age. Apparent photosynthesis (AP) and translocation of assimilated ¹⁴C were determined on leaves 3, 5, and 8 from the tip of a cotyledonary lateral branch of the “Florunner” cultivar of peanut (Arachis hypogaea L.) at 80, 110 and 140 days after planting. To determine ¹⁴C-photo-synthate translocation individual leaves were exposed for 15 min to ¹⁴CO₂ and plants harvested 24 hr later were analyzed for ¹⁴C. Translocation was computed as the percentage of total ¹⁴C in the plant which was in plant parts other than the labeled leaf.

Highest AP was observed for leaf 3, the youngest fully expanded leaf on the branch, and the lowest AP for leaf 8. Leaf 5 exhibited intermediate AP rates. AP decreased with plant age, the average decrease in two experiments being 21 and 58% from 80 to 110 and 140 days, respectively. The decline in AP with plant age was similar in both experiments. The percentage of ¹⁴C translocated from labeled leaves for the two experiments averaged 64% and was not significantly affected by plant age. A significantly greater percentage (76%) of the ¹⁴C fixed was translocated from leaf 3 in Experiment II than from leaves 5 and 8 which averaged 55%. Leaf position had no effect on ¹⁴C translocation in Experiment I. These data indicate that leaves near the periphery of the peanut plant contribute most during pod filling and that the photo-synthetic capacity of all leaves decreases during this period.