Callose Walls in Megaspores inFuchsiaandEpilobium

SUMMARYIn Fuchsia hybrida and Epilobium palustre callose occurs in the entire cell wall of the megasporocyte at the first meiotic prophase. After a short period callose disappears from the micropylar apex of the cell. This apex remains free of callose during megasporogenesis, whereas callose is present in the cross and side walls and at the chalazal end of a tetrad.Inactive megaspores with callose walls persist in ovules when the embryo sac is developing from the micropylar megaspore. A row of three inactive megaspores is attached to the chalazal pole of the developing embryo sac. In Epilobium, callose in cross walls is partially hydrolized and sites without callose occur. The cross walls of the inactive megaspores are then similar to sieve plates. The passage of materials from degenerating, inactive megaspores into the developing embryo sac may thus be possible.