SCHIZOGENY AND ULTRASTRUCTURE OF DEVELOPING LATEX DUCTS IN MAMMILLARIA GUERRERONIS (CACTACEAE)

The schizo-lysigenous latex ducts of Mammillaria guerreronis, sect. Subhydrochylus, were examined by optical and electron microscopy. These ducts are complex having a distinct outer epithelium without intercellular spaces and an inner epithelium in which schizogenous spaces arise. Schizogeny begins with formation of bulbous pockets and/or production of dark streaks in certain walls. Spaces formed by these processes ultimately contain a combination of electron dense materials, vesicles, and numerous thin, convoluted wall layers. Schizogeny may be responsible for initial formation of lumen and latex and may also separate some inner epithelial cells from the surrounding layers. Lysigeny of the inner epithelial cells contributes materials to the latex and allows enlargement of the duct. The inner epithelial cells contain mitochondria, dictyosomes, apparently functional nuclei, and numerous vesicles. The outer epithelium has fewer vesicles than the inner epithelium. Schizo-lysigeny in the members of sect. Subhydrochylus is considered to be ancestral to the strict lysigeny of the members of sect. Mammillaria. The inner and outer epithelia of M. guerreronis are thought to be homologous to the lumen and epithelium respectively of M. heyderi.