Summary Studies of the absorption and translocation of 14C‐2,4‐D in Chenopodium album L., Galinsoga parviflora Cav., Datura stramonium L. and Galium aparine L. in relation to their susceptibility gave the following results: In G aparine (resistant) there was little transport of 2,4‐D applied to the leaves, and a probable relationship between resistance and the immediate binding of the 2,4‐D in the treated leaf. D. stramonium (relatively resistant) transported 2,4‐D in considerable amounts alter uptake through the leaf, while C. album (very susceptible) and G. parviflora (susceptible) were intermediate in respect of 2,4‐D translocation. No relationship between susceptibility of these four species and 2,4‐D uptake and translocation from the leaves could be established. After application to the root systems of the four species, 2,4‐D was taken up and translocated in the shoot to varying extents. In G. aparine much 2,4‐D was taken up and translocated. In contrast to leaf application, the herbicide was not immediately converted into a strongly‐held immobile form. In C. album, G. parviflora and D. stramonium, however, no 2,4‐D was translocated in the shoot. There was thus no correlation between susceptibility and shoot transport of 2,4‐D in the four species studied. Distribution du 2,4‐D marqué au 14C dans des espèces de mauvaises herbes présentant des sensibilités diverses

Summary Studies of the uptake and translocation of 14C‐labelled 2, 4‐D, MCPA and aminotriazole in Agrostemma githago L. and Tussilago farfara L. clarified the behaviour of the herbicides in both species. In A. githago, MCPA was more freely mobile than 2,4‐D after application to the leaf; it was distributed in the plant more rapidly and in greater quantity. Similarly, following root uptake MCPA was transported in the shoot in greater amounts than was 2,4‐D. There is a clear relationship between the susceptibility of A. githago to MCPA and the mobility of the herbicide in the plant. In T. farfara, 2,4‐D and aminotriazole applied to the leaves were equally well absorbed and relatively rapidly translocated. During the period up to 72 h the amounts of herbicide in the plant increased to similar levels; after that, 14C activity in plants treated with 2,4‐D fell slightly whereas there was further accumulation of aminotriazole. Following uptake through the roots, translocation and accumulation in the leaves were considerably greater with aminotriazole than with 2,4‐D. The lack of accumulation of 2,4‐D could be a factor in the resistance of T. farfara to this herbicidie. Recherches sur l'absorption et la migration d'herbicides marqués au 14 C dans Agrostemma githago L. et Tussilago farfara L.