AbstractUsing seedlings ofRicinus communisL. sucrose export from the cotyledons to the hypocotyl and roots was measured at different levels of sucrose concentration in the cotyledons. Sucrose export followed Michaelis‐Menten kinetics with a half‐saturation of export at 35 mM sucrose in the cotyledons. A maximal export flux of 90 μmol h−lg−1fresh weight of the cotyledons was obtained. Both these figures coincide with those obtained for sucrose uptake into the cotyledons. It is postulated that sucrose uptake and sucrose export occurs by the same mechanism and possibly by the same cells which then would have to be part of the phloem. Since sucrose uptake has been shown to proceed as proton‐sucrose co‐transport, phloem loading might also be energized by the protonmotive potential difference. The data, furthermore, are difficult to reconcile with the symplastic route of ph