Some Characteristics of Photosynthesis and Nitrogen Fixation in Heterocysts Isolated by Digitonin Interaction of Two Populations of the Blue-Green Algae in Co-Culture The Effects of Immobilization on Photosynthesis, Growth, Nitrogen Fixation and Ammonium Ion Excretion of Mutant and Wild Type Cells of Anabaena variabilis Studies on Substitutions Among Mn, Ca and Mg Ions and Oxygen Evolution of Anabaena Variabilis