14 C‐Studies on Apple Trees. IV. Photosynthate Consumption in Fruits in Relation to the Leaf‐Fruit Ratio and to the Leaf‐Fruit Position

The photosynthate consumption in apple fruits in relation to the leaf/fruit ratio was studied in sections of branches of the Graasten and Golden Delicious varieties by exposure to 14 CO 2 during July and August. A significant, negative correlation was found between the fixation of 14 C in the fruits in terms of percent of the total amount of 14 C absorbed and the leaf/fruit ratio of the branch sections. The leaf area required for the saturation of one fruit was found to be ca. 190 and 230 cm 2 (14 and 17 leaves) in the case of Golden Delicious, and ca. 400 and 670 cm 2 (25 and 42 leaves) for Graasten in July and August, respectively, calculated under conditions of large leaf areas per fruit. In such cases a fairly good, reverse proportionality exists between the 14 C fixation in the fruit in terms of percent and the leaf area expressed in multiples of saturation area. At low leaf/fruit ratios, however, the actual saturation area is found to be lower than the theoretically computed one. The translocation of the 14 C assimilated in the leaves of the extension shoots or of spurs without fruits to fruits on other spurs was on the whole promoted by a decreasing leaf/fruit ratio in the parts in question; similarly the greatest transport took place on the side where the leaf/fruit ratio was lowest. The fixation was often greatest in the fruit closest to the treated leaves, hut in a number of cases the value was higher for the second closest or even further removed fruits. In this connection the importance of the size of the fruit and the vascular connections is discussed.