Abstract: Scanning electron microscopy was used to follow the fate of Anabaena azollae in Azolla microphylla, A.filiculoides and A.mexicana, and mechanism by which the endophytic Anabaena were partitioned into developing sporocarp.Two kinds of algal hormogonia were found in close association with the trichomes around the base of the sporangial primordia.Most of Anabaena fila-ments entered the developing sporocarps through the pore of the tip in the indusia.But a possibility that the filaments passed through the pore of the base of the developing sporocarps could not precluded as well.The actively dividing vegetative cells of the endophyte were observed inside the developing sporocarps, none of the akinets of Anabaena, however could be seen outside the developing sporocarps.Occasionally, some of the vegetative cells were engulfed in the inner layer cells of the indusium in the nearly matured megasporocarps.