These, as in Gymnosperms, are of two kinds, microspores or pollen-grains, borne in the stamens (or microsporophylls) and megaspores, in which the egg-cell is developed, contained in the ovule, which is borne enclosed in the carpel (or megasporophyll).
It has been shown by Lawson that in Sequoia sempervirens (Annals of Botany, 1904) and by other workers in the genera that several megaspores may attain a fairly large size in one prothallus.
The spores produced in each sporangium vary from very many to a single one in the case of some heterosporous forms. These latter bear spores of two kinds, microspores and megaspores, in separate sporangia.
Some Calamites were heterosporous, sporangia with microspores and megaspores being found in the same cone.
In the megasporangium, on the other hand, the four megaspores, which arise from a single mother-cell, are nourished at the expense of the other sporogenous cells and of the tapetum.