14 C‐Studies on Apple Trees. VI. The Influence of the Fruit on the Photosynthesis of the Leaves, and the Relative Photosynthetic Yields of Fruits and Leaves

When paired samples of either intact or detached apple shoots with and without fruits were exposed simultaneuosly to 14 CO 2 , the uptake of 14 CO 2 of leaf area was found to be greater in the fruit‐bearing shoots, often by a factor of 1.5 or more, although the difference tends to be slight or even non‐existent when the experiments follow shortly after a previous dark period. The uptake of 14 CO 2 by photosynthesis in the skin of detached fruits is very slight compared to the simultaneous uptake of 14 CO 2 by the leaves from the same spur, and can hence contribute only slightly to the development of the fruit compared with the supply of assimilates taking place from the leaves to the fruit.