Structure and chemical composition of the spore wall in Spirogyra (Zygnemataceae, Chlorophyceae)

Spores of twenty species of Spirogyra were treated by acetolysis and viewed by scanning electron microscopy. The terms exo-, meso- and endospore should be maintained and based on chemical composition. Exo- and endospore are cellulose and/or pectin containing membranes. The mesospore is acetolysis-resistant and presumably contains sporopollenin. As basic pattern the spore wall in Spirogyra is composed of four layers; one exo- and endospore layer and two mesospore layers. The outer mesospore layer is mostly thin and hyaline, the inner layer thick and brown or yellow coloured and often sculptured. The germination suture is located in the inner mesospore layer. Some variations on this basic pattern were observed in Spirogyra bellis, S. cleveana and S. majuscula. Details of mesospore sculpture were observed and some taxonomic implications are discussed. The observed basic pattern is assumed to be valid for the Zygnemataceae as a whole.