. Bulletin of the British Museum (Natural History) Botany. . Fig. 30 Pollination of unspecialised Hypericum flowers (one sepal and two petals removed): (a) H. calycinum (x 2-5); (b) H. perforatum (x 4). As the outer stamens move inward, the anthers come into contact with the stigmas, thus ensuring self-pollination if cross-pollination has not occurred (Fig. 30b). In some species ( H. linarifolium and H. humifusum, sect. 14. Oligostema), unfavourable weather conditions result in pseudocleistogamy, the flowers do not open and are automatically self-pollinated (Ivimey-Cook, 1963). The st
. Bulletin of the British Museum (Natural History) Botany. . Fig. 30 Pollination of unspecialised Hypericum flowers (one sepal and two petals removed): (a) H. calycinum (x 2-5); (b) H. perforatum (x 4). As the outer stamens move inward, the anthers come into contact with the stigmas, thus ensuring self-pollination if cross-pollination has not occurred (Fig. 30b). In some species ( H. linarifolium and H. humifusum, sect. 14. Oligostema), unfavourable weather conditions result in pseudocleistogamy, the flowers do not open and are automatically self-pollinated (Ivimey-Cook, 1963). The styles in bud are erect and in contact with the anthers. In primitive species they remain erect or more-or-less united, so that no movement is necessary for self-pollination to occur, other than a slight outcurving at the tip. In several sections ( 10. Olympia) the petals close up as well as the stamens, resulting in a second bud-like stage of anthesis. This movement, however, does not appear to be necessary to ensure self-pollination (although it may help to produce it), as the species in which the petals and/or stamens are deciduous ( in sect. 3. Ascyreia) are not noticeably less fertile, under similar conditions, than those with a second bud-stage. (b) Insect visitors Such flowers as those that have just been described are typically visited by the less- specialised insects, of which the Syrphidae (Diptera) are the commonest visitors to Hypericum. They are particularly associated with yellow flowers (Faegri & van der Pijl, 1971), and the well-known irregularity of their visits may have been a factor in the evolution (? or retention) of a self-compatible breeding system. Bombylids, which are also frequent visitors, are more specialised; but they commonly visit primitive flowers for pollen. Muller (1883), moreover, observing that these flies frequently put their tongues into the flowers of. Please note that these images are extracted from scanned page images that may
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