Bryophytic spores of eight genera in the sub-order Jungermanniales acrogynae have been examined by transmission electron microscopy. The spores are alete and subisopolar, ranging in size from 8–50 μ. Although most of these spores are indistinguishable from one another under the light microscope, great variation of wall structure can be detected at the electron microscope level. Three elements of fine structure are defined: sheet lamellae, slip lamellae and microgranules. Slip lamellae are found in all eight spore types, but sheet lamellae are lacking in the Lophocoleaceae. The lamellae have a thickness of 20–30 nm with a central low-dense region about 4 nm thick. A homogeneous sporonine material is present in walls ofRadulaandFrullaniaspores. Similar wall ultrastructure is exhibited among members of a family; two genera have been studied from each of the families Lophocoleaceae and Cephaloziaceae. Preparative techniques are discussed and comparisons drawn with the fine structure of pollen walls.