Experimental crosses between Salix discolor, S. petiolaris, S. bebbiana, and S. lucida resulted in the synthetic hybrids S. discolor × petiolaris and S. bebbiana × petiolaris and their reciprocals. The cross S. bebbiana × discolor and all crosses involving S. lucida were unsuccessful. Field experiments on the mode of pollination of Salix revealed the presence of wind-borne pollen of S. discolor, S. petiolaris, and S. bebbiana, and seed was set by these species in the absence of insect vectors. They are suspected to be both entomophilous and anemophilous. Salix lucida did not set seeds under these conditions and it is hypothesized that it is fundamentally entomophilous. Evidence is presented that suggests that natural hybridization between S. discolor and S. petiolaris may be restricted by differences in flowering time and by pollen competition.