Samples of chasmogamous flowers of three species of Viola from seven different habitats were examined for the contents of their stigmatic cavities. Flower and pollen morphology are described. Insect exclusion experiments suggest that self-pollination is rare and emasculations have established that intraspecific and interspecific pollen transfer is frequent. The quantity of pollen introduced into the stigmatic cavity is affected by several factors. Rain reduces pollination in exposed habitats and similar decreases are detected in sheltered or north-or east-facing habitats due to the smaller amount of sunlight incident upon them. Percentage pollination remains high in habitats with no blossoms of other genera; anthophilous insects visit Viola for food. Habitats with a variety of blossoms besides Viola may lure sufficient insects to ensure the pollination of all species, including the inconspicuous ones. However, large stands of showy blossoms may monopolize the insect visitors in a habitat also occupied by less attractive species. It is argued that gene flow in disturbed or marginal habitats may be increased by the greater availability of potential pollinators.
Beattie, A. J., "Studies in the Pollination Ecology of Viola. 1. The Pollen-content of Stigmatc Cavities" (1973). Ba. Paper 9.
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