The tip cells of antheridia of Polytrichum juniperinum

Abstract

As in other mosses, the opening of an antheridium for sperm release in Polytrichum occurs with the swelling of thickened walls in the cells at the tip of the antheridium. Although the tip cells are distinguishable by their shape and slightly thicker walls at early stages of development, the addition of the wall layer that swells seems to occur only during the last few 10ths of a millimetre of antheridial elongation. Changes in the vacuome and the accumulation of cytoplasmic vesicles differentiate the cytoplasm of tip cells from that in other jacket cells, but dictyosomes are few or absent in tip cells. Autophagic activity occurs in the protoplasts of tip cells as they near maturity.