Pollination Drop and Microdrop Secretions in Cedrus

In Cedrus pollen adheres by microdrops to the apical portion of the integument. The microdrops originate from dictyosome vesicles in cells of the integument apex. Electron-dense substances are present in these dictyosome vesicles and accumulate between the surface cell walls and plasma membrane. The substances traverse the walls and form microdrops. The cuticle layer on the surface cell walls is less developed and does not serve as an obstacle to the passage. During pollination drop secretion, nucellar cells show characteristics such as undulation of the plasma membrane, numerous dictyosomes, and a prominent amount of endoplasmic reticulum. The cuticle layer is absent from the nucellar apex. After the secretion, cell walls of the nucellus and chalaza become transparent. We describe ultrastructural changes associated with the winter dormancy of the ovule.