Abstract
Some species produce pollen grains with different aperture numbers within a single individual (pollen aperture heteromorphism). In the pansy Viola diversifolia, aperture number is positively correlated with pollen germination speed, and negatively correlated with viability. In V calcarata, young five-aperturate pollen grains germinate faster than four-aperturate ones. Heteromorphism could thus be favoured when pollination is unpredictable, as plants produce both very competitive and long-lived pollen grains. Depending on the efficiency of the pollinators, different proportions of pollen types will be optimal. In insect-pollinated species, such as V:calcarata, pollination efficiency generally decreases as elevation increases. We therefore expect a decrease in mean aperture number as altitude increases. This was found in four transects tout of six). Pollinator activity therefore has a potential impact on pollen morphology. (C) Academie des Sciences/ Elsevier, Paris.