Ultrastructure and Differentiation of Hydrodictyon Reticulatum II. Formation of Zooids Within The Coenobium

Abstract

A summary of the life cycle of H. reticulatum is given here in the second of a series of papers on an ultrastructural study of the development and differentiation of the various stages in the life cycle. The formation of zooids by the coenobia is then discussed in detail. After the fragmentation of the chloroplast and disintegra. tion of the pyrenoids the cytoplasm cleaves: firstly, to form the vacuolar envelope, a thin cytoplasmic layer that separates the vacuole from the rest of the cytoplasm; secondly, to form uninucleate fragments of the cytoplasm each of which later develops a pair of flagella. Observations on the cytoplasmic cleavage and the role of microtubules in the cleavage are related to similar events in other algae. The function of the vacuolar envelope and the golgi apparatus, and the disintegration of the pyrenoids are also discussed.