Comparative Anatomy of Pollinia and Caudicles of an Orchid (Epidendrum)

Abstract

The developing pollinia and caudicles of an orchid (E. ibaguense) were studied using light, transmission electron, and fluorescence microscopy. Both types of cells originate as meristematic masses in the microsporangium. After several mitoses, the pollen mother cells enter meiosis, and synaptonemal complexes are observed. At the same developmental stage, the caudicle cells enter a division cycle similar to meiosis. Deposition of callose in the cell walls is observed. Completion of meiosis is marked by simultaneous cytokinesis to produce tetrads. Spherical tetrads make up the bulk of the pollinia, whereas the caudicles contain primarily linear tetrads. Tetrad formation is followed by a mitotic cell division to produce a small, dense cell within each tetrad member. Deposition of a thick secondary wall on cell walls not immediately adjacent to each other in both pollinia and caudicles completes the development. The close developmental and structural similarities between caudicles and pollinia offer proof of the theory that the caudicle evolved from a pollinium.