Illustration of a "Geosiphon pyriforme" siphonal bladder. "pc"N":"Nostoc" cell wall, "N":"Nostoc" filament, "he":heterocyst, "ms":simbiosome membrane, "pm":plasma membrane, "pc"G":"Geosiphon" cell wall, "nu":nucleus, "mi":mitochondrion, "in":cytoplasmatic inclusions, "va":vacuole.