Distribution of 14C-labelled Products of Photosynthesis during the Commercial Life of the Tomato Crop

On seven occasions measured amounts of ¹⁴CO₂ were supplied toindividual leaves on tomato plants grown as a crop under commercialconditions. Twenty-four hours later the distribution of radiocarbonproducts was determined using counting procedures. In the vegetativephase lower leaves exported more carbon up than down, and upperleaves a larger proportion downwards. During the developmentof the crop upper leaves continued to export more carbon downthan up, and lower leaves developed a similar tendency. In theyoung fruiting crop all leaves supplied all the trusses, butas the number of trusses increased groups of leaves came tohave primary (but not absolute) responsibility for supplyingsingle trusses. At the time of fruit development the leavesretained for 20–24 hours more than 80 per cent of thecarbon they fixed. Mature leaves and stems both above and belowthe test leaves were significant sinks for ¹⁴C products.