STRUCTURAL DEVELOPMENT OF THE CAUDICLE OF AN ORCHID (EPIDENDRUM)

Structural changes during development of the caudicle of Epidendrum ibaguense (Orchidaceae) were followed using light and electron microscopy. The caudicle begins as a mass of small meristematic cells in the microsporangium. The central cells of the mass enlarge and enter a division cycle. Completion of this cycle produces linear tetrads of cells which remain attached to each other throughout the life of the caudicle. These tetrads then accumulate a thick secondary wall on their outer surfaces. These thick-walled cells form the main structural element of the caudicle at maturity. The cells on the periphery of the mass differentiate into a gradation of cell types characterized by their very high content of smooth ER. The majority of these thin-walled cells are located at the junction points between adjacent caudicles and between caudicle and pollinium. The cells in these positions produce large quantities of a lipid polymer. This product is synthesized in association with large tubular ER complexes present in discrete areas in the cytoplasm. Plastids of these cells also produce a lipidic substance. Some thin-walled cells are located among the thick-walled structural cells; however, the lipid polymer is not synthesized in these cells. At maturity, all thin-walled cells undergo breakdown and autolysis resulting in gradual obliteration of cytoplasmic detail and organelles. In the lipid containing thin-walled cells, lysis of the cells releases the lipidic masses which then form the elastic joining compound between adjacent caudicles and between caudicles and pollinia.