 If it does occur , protandry does nothing to prevent geitonogamous self @-@ pollination : that is , pollination with pollen from another flower on the same plant . In fact , when birds forage at B. prionotes , only about a quarter of all movements from inflorescence to inflorescence involve a change of plant . Geitonogamous self @-@ pollination must therefore occur more often in this species than cross @-@ pollination . This does not imply high rates of self @-@ fertilisation , however , as the species appears highly self @-@ incompatible : although pollen grains will germinate on flowers of the self plant , they apparently fail to produce pollen tubes that penetrate the style . Even where cross @-@ pollination does occur , fertilisation rate is fairly low . It is speculated that this is related to " a variety of chemical reactions at the pollen @-@ stigma interface " . 
