Selaginella is heterosporous, the megasporangia being often found towards the base of the cone.
The development of the microand megasporangia is the same up to the stage of isolation of the spore mother-cells.
They consist either of microsporangia or megasporangia, which are arranged in basipetal succession on the receptacle.
Each sorus includes both microsporangia, with numerous spores, and megasporangia, each of which contains a single megaspore with a complicated wall.
The abortion of certain spores, which is known to have taken place both in the homosporcus C. Binneyana and in the megasporangia of C. Casheana, may throw some light on the origin of the heterosporous condition.