Electron Microscopic Study of Heterocyst Development in Anabaena Azollae Strasburger1

SUMMARY Various stages of heterocyst development in Anabaena azollae growing within Azolla filiculoides were viewed with an electron microscope. Developing heterocysts undergo marked internal and external reorganization which cannot be detected with light microscopy. The proposed sequence of developmental stages includes: (1) formation of a thick, two‐layered envelope; (2) contortion of photosynthetic lamellae; (3) loss of granular inclusions and possible loss of or change in nucleoplasms material; and (4) concentration of photosynthetic lamellae toward the poles. These findings are compared with those reported by Wildon and Mercer in 1963.