Abstract: This paper presents a detailed report on the developmental progresses of the microsporangium and its microspores in Azolla filiculoides Lam., and shows the morphologicaI structures of the respective developmental stares with the aid of scanning electron photographs. The entire developmental progress may be divided into six stages: ( 1 ) The microspore mother cell initiating stage The microsporangium initial on the placenta of the sporocarp gave rise a sporogenous cell, and then divided four times to form sixteen microspore mother cells; (2) The meiotic stage–The microspore mother cells initiated meiosis inside their calIose walls. The radial and inner tangential walls of the tapetum were dissolved at the same time and followed by the formation of a sporoplasmodium; (3) The microspore shrinking Ⅰ–After the callose walls of tetrads was dissolved, those microspores that just released from the callose walls shrunk intensely and became spherical later again. The sporoderm of microspores was principally synthesized in this stage, and the volume of microspores became evidently increased. The microspores then gradually moved to the periphery of the sporoplasmodium; (4) The microspore shrinking Ⅱ-Each microspore formed a large vacuole and gave rise the second contraction. The periphery of the sporoplasmodium was gradually dissolved; (5) The massulae forming stage–The sporoplasmodium was dissolved successivelly, and the undissolvable granules and organelle membrane residues. became aggregated into the compartmental layer, and the microsporangium was divided into several large vesicles, each vesicle will form a massulae; (6) The microspore germinating stage–The ,natured microspores inside the massulae each gave rise an androgonial initial which divided two times to form four antherozoid mother cells and then gave rise the antherozoids. The relationships between the various morphological structures and their functions in the microsporangium developmental progress have breify discussed. In addition, our viewpoints have compared with those of previous investigations.

Key words: Azolla, Microsporangium, Microsporogenesis