Abstract: Pullen grains of 2 genera 31 species of the family Salicaceae ia Gansu have been investigated. The comparative studies of the pollen grains were carried out by means of seanning electron microscope and light microscope. The two genera (Popu- lus L. and Salix L.) can be distinguished by their pollen characters such as the shape of pollen, type of aper ure, ornamentation of exine etc. 1. Shape of pollen grains 1) Spherical (rounded) : Populus L., 2) Ellipoidal, (subrotund): Salix L. 2. Type .of aperture 1) Atreme: Populus L., 2) 3-colpate, 3-colporoidate or 3-syncolpate: Salix L. 3. Ornamentation of exine 1 ) Cavernulous: Populus L., 2) Tubercular: Populus L., 3) Spinulate: Salix L., 4) Rugulose: Populus L. and Salix L., 5) Finely-reticulate: Populus L., 6) Reticulate: Salix L., 7) Crass-reticulate: Salix L., 8) Rugulose-Spinulate-Cavernulous: Salix L., 9) Rugulose-Reticulate: Salix L. Basing upon the above pollen characters, the genera Populus L. and Salix L. are con- sidered two good and natural taxa, and the genus Populus L. is more primitive than the genus Salix L.

Key words: Salicaceae, Populus, Salix, Pollen morphology