Comparative development of the sporophyte-gametophyte junction in six moss species

Developmental anatomy of the sporophyte-gametophyte junction in six moss species is described with special reference to sporophyte penetration into the gametophytic tissue. The sporophyte-gametophyte junction in mosses is classified into two types based on vaginula morphology: in the true vaginula type, the junction involves only an epigonium derived from the archegonium, and in the other shoot vaginula type, it involves a shoot and an epigonium. In both of the types, the sporophyte penetrates into an epigonial tissue accompanied by degeneration of epigonium cells under the developing sporophyte. In the shoot vaginula type, the sporophyte further penetrates into the conducting strand or similar cells that seem to be induced by stimulation of fertilization. It is likely that the difference in growth rate between the epigonium and the capped sporophyte is a mechanical force for sporophyte penetration.