1. The embryo of Reboulia develops without the formation of an octant stage characteristic of certain other Marchantiaceae. 2. The first transverse wall in the fertilized egg separates the cell which is to form the foot from that which is to form the seta and capsule. Four horizontally superimposed cells are usually formed, each new division occurring in the outermost segment. Of these the lowest cell forms the foot, the next one the seta, and the upper two the capsule. 3. The sporogenous tissue is formed relatively early in the history of the sporophyte. 4. In the development of spore mother cells and elaters the walls around the sporogenous cells become mucilaginous, the protoplasts of the former assume an amoeboid form and finally become large and spherical, while those of the latter are slender and elongated. A new cell wall is laid down around both spore mother cells and elaters. 5. The assumption of an amoeboid form by the young spore mother cells is a feature related to their nutrition. 6. An elate...