Ultrastructure of pericarp development in Gracilaria verrucosa (Hudson) Papenfuss (Gracilariaceae, Gracilariales, Rhodophyta)

BY : S. G. DELIVOPOULOS

The ultrastructure of pericarp development in Gracilaria verrucosa (Huds.) Papenfuss is described. Anticlinal and successive periclinal divisions of the outer cortical cells result in the formation of a thick multilayer pericarp. Primary pit connections occur between pericarp cells. Mucilage is formed within cytoplasmic concentric membranes, giving thus rise to mucilage sacs. In addition, mucilage sacs seem to arise through local dilations of the nuclear envelope. Mucilage sacs considerably increase in volume resulting in the formation of one or two huge mucilage sacs, which occupy the major part of the cell interior and finally discharge their contents. Thus, inner pericarp cells actually function as secretory cells exhibiting a degenerate appearance after the release of the content of mucilage sacs.