Cellular differentiation of heterospory inSelaginella

Summary Selaginella pilijera consistently displays two rows of microsporangia and two rows of megasporangia. It is therefore possible to detect in longitudinal sections of strobili at least three significant differences in development between both types of sporangia prior to meiosis: size of young sporangia, abortion or development of sporocytes based an RNA staining, and presence or absence of callose walls around sporocytes. The functional significance of these differences is discussed in relation to the heterosporous habit and higher plant sporogenesis.