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The ordinary mycelium is the gametophyte since it bears the ascogonia and antheridia when present; the ascogenous hyphae with their asci represent the sporophyte since they are derived from the fertilized ascogonium.

The matter is complicated by the apogamous transition from gametophyte to sporophyte in the absence of the ascogonium; also by the fact that there are normally two fusions in the life-history as mentioned earlier.

E, F, Sections of young perithecia. w, Parietal cells. f, Pseudo-parenchyma. as, Ascogonium.

In all these cases the ascogonium and antheridium contain numerous nuclei; they are to be looked upon as gametangia in which there is no differentiation of gametes, and since they act as single gametes they are termed coenogametes.

The cytological details of development of the perithecia are not well known; most of them appear to develop their ascogenous hyphae in an apogamous way without any connexion with an ascogonium.