Abstract:The gametophytic development and apogamy of the fern Onychium siliculosum(Desv.) C. Chr. were observed by microscope and semithin section technique. The results exhibited that the spores are tawny, tetrahedral, and trilete. During the period of germination a rhizoid was produced firstly, then the prothallial initial cells. The germination was of the Vittaria-type. The prothallial cells, after experiencing the stages of filament and thallus, developed into prothallium. The pattern of the prothallial development was Ceratopteris-type. The filaments were rich in branches and they formed cluster prothallia. Antheridia were generated on the prothallia, but no archegonia were formed through repeated experiments. This species belonged to obligate apogamy. The observation of semithin section showed that the apogamous embryo is caused by the divisions of a group of small cells, which originated from the gametophytic cells behind the apical notch of the prothallium. The apogamous bud was differentiated first from the small cells, and then the root. The apogamous bud and the embryo root were connected by the differentiated vessels which also connected the gametphyte and the sporephyte.