Reproduction in blue-green bacteria is primarily asexual (e.g., fission, fragmentation). There is some evidence for bacteria-like conjugation. Because the cells are prokaryotic, there are no nuclei, no chromosomes, no mitoses or meioses, and no mitochondrial or chloroplast double membranes. Chlorophyll a and phycobilins are the photosynthetic pigments. Food reserve is glycogen. Cell wall chemistry is bacteria-like. No cells within this group are flagellated. A representative member of the group is Oscillatoria (Fig.1), a common blue-green with small prokaryotic cells stacked end-to-end. Most blue-green algae are planktonic and contribute to lake and ocean productivity. Some blue-green algae make significant contributions to global nitrogen cycling. Some fowl waters in surface "blooms", while others find their way into health food stores as dietary supplements. This group is a very old one, with little apparent change in morphology over a 2 billion-year period. There are approximately 1,275 species within the group.