a1 Department of Botany, Faculty of Science, University of Khartoum, Khartoum, Sudan
Selected leaves of broad bean on separate plants were supplied with 14CO2, at four stages during development and the distribution of radiocarbon products determined quantitatively 24 h later. These leaves retained substantial amounts of the radiocarbon they fixed initially. In the vegetative phase, basal and middle leaves exported more carbon up than down while the apical leaves exported mainly downwards. During the flowering and pod-setting phase, basal and middle leaves exported carbon equally up and down whereas the apical leaves continued to export mainly downwards. Since assimilates produced by basal, middle and apical leaves at any developmental stage in the life of the broad bean plant were moved both acropetally and basi-petally, it must be concluded that bidirectional transport of assimilates occurred in the stem. During the life of the crop all sources supplied assimilates to all sinks.
(Accepted April 10 1984)
p1 Present address: Department of Botany, Faculty of Science, University of Qatar, PO Box 2713, Doha, Qatar, Arabian Gulf.