STRUCTURAL DEVELOPMENT OF THE CAUDICLE OF AN ORCHID (EPIDENDRUM)

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Abstract
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.
Funding Information
  • Natural Sciences and Engineering Research Council (A6704)