Abstract: The occurrence and development of the hair ceils on the shoot tips and in the leaf cavities of A. filiculoides, A. microphylla, A. pinnata and their algae-free cultures were examined by means of scanning electron microscopy with microdissect technique. The patterns of Anabacna moving into the leave cavities from the shoot tips were investigated on three species of Azolla during their vegetative growth. The results showed that the patterns of symbiotic Anabaena infecting the leaf cavities are similarity among three species of Azolla and may be divided to the four phases which are summarized as follows: 1. occurrence of primary branched hair and adhesion of Anabaena; 2. development of primary branched hair and spreding of Anabaena; 3. building of hair bridge and entrance of Anabaena into the cavities; 4. formation of secondary simple hair and transference of Anabaena within the cavity. These observations resulted in a hypothesis that hair induces and leads its partner. It is suggested that the hair cell is likely to be a structure of Azolla for attracting and recognizing its symbiont in addition to transport substance between fern and algae.

Key words: Azolla, Anabaena, Relationship