Pollen grains of 10 anemophilous and entomophilous species of angiosperms were kept at 4 relative humidities (RH) (15, 51, 79 and 98%) and their viability tested by fluorochromatic reaction after time lapses ranging from 6 to 144 h. Pollen viability in the anemophilous species decreased more rapidly than in the entomophilous ones with the exception of the dioecious palmChamaerops humilis. The modes of anther and flower opening, times of anther exposure etc. were recorded: Cytological data are discussed and compared with these aspects of reproductive ecology.