POLLEN DEVELOPMENT AND FERTILIZATION IN LACANDONIA-SCHISMATICA (LACANDONIACEAE)

The flower of Lacandonia schismatica is bisexual. Three or sometimes f our bilocular or trilocular anthers occupy the center of the flower in side the zone of carpels. The anther wall comprises four layers: epide rmis; endothecium whose cells develop helical wall thickenings; one mi ddle layer, which disappears early; a tapetum of the secretory type. T he 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: epi dermis and endothecium. The pollen grain is three-celled by the time g ermination occurs. Anther dehiscence has not been observed and probabl y does not occur. Pollination of Lacandonia schismatica occurs in the unopened flower bud. The pollen grains germinate within the anthers, w hich do not dehisce, and the pollen tubes grow within the receptacle u ntil they reach the ovules. The pollen tube enters the embryo sac thro ugh the micropyle and one synergid, and fertilization is completed by anthesis. This reproductive pattern conforms to Lord's definition of p reanthesis cleistogamy.