Abstract: The structure of Azolla pinnate leaves was examined by means of light and transmission electron microscopy. Emphasis was put on the ultra structural cytology of leaf cavity hairs both in association with Anabaena and in Anabaena-free cultures of Azolla and on the roles of the hair in substance change between the symbionts. The cavity hairs were multicultural and branched. There were numerous mitochondria, plastids, endoplasmic reticular and ribosome’s in the cytoplasm of the hair. A. marked characteristic of the hair was the cell wall ingrowths; There were large electron-transparent area between the in growing cell wall and the plasmolemma. Some vesicles were found in this area. It was suggested that these vesicles as transporters played the role in transporting substances. Electron microscopy revealed that some differences were present between the basal cell and the terminal branched cell of the hairs. In the latter, the cytoplasma, organelles, growing wall and vesicles were richer in the electron-transparent area than in the former This feature of the terminal branched cell showed that the terminal cell of the hair was more active in absorption and/or secretion of metabolites than that of the basal cell. Some hairs were found near the stem apex of Azolla. It was suggested that these hairs functioned in supplying the nitric compounds for the algae living on the stem apex of Azolla. These algae had no ability to fix nitrogen because of lacking heterocyst. In the absence of Anabaena azollae, the leaf cavity hairs were still present in Azolla pinnata. However, a lot of osmiophilic substances can often be seen in the vacuole of this hair.

Key words: Azolla, Symbiotic Relationship