[Identification of tritiated assimilales within the sieve tubes of cucurbita pepo]

After application of D-glucose-6-T to small areas of leaf surfaces of Cucurbita, radioactivity - mainly sucrose-T - could exclusively be localized by histoautoradiography ("dry-technique") within single sieve tubes of exporting bundles. The centre of activity corresponded to the "slime"-plugs (in crosssection-autoradiograms) of the sieve tubes and to the sieve plates (in longitudinal sections). It is concluded that only the sieve tubes are the conducting channels for the long-distance transport of those substances which are labeled with tritium in these experiments.