POLLEN DEVELOPMENT AND FERTILIZATION IN LACANDONIA-SCHISMATICA (LACANDONIACEAE)

The flower of Lacandonia schismatica is bisexual. Three or sometimes four bilocular or trilocular anthers occupy the center of the flower inside the zone of carpels. The anther wall comprises four layers: epidermis; endothecium whose cells develop helical wall thickenings; one middle layer, which disappears early; a tapetum of the secretory type. The tapetal cells apparently form cytoplasmic bridges among themselves. The microspore tetrads are in an isobilateral arrangement, surrounded by a thick wall. The mature anther wall has only two cell layers: epidermis and endothecium. The pollen grain is three-celled by the time germination occurs. Anther dehiscence has not been observed and probably does not occur. Pollination of Lacandonia schismatica occurs in the unopened flower bud. The pollen grains germinate within the anthers, which do not dehisce, and the pollen tubes grow within the receptacle until they reach the ovules. The pollen tube enters the embryo sac through the micropyle and one synergid, and fertilization is completed by anthesis. This reproductive pattern conforms to Lord's definition of preanthesis cleistogamy.