ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE ANTHOCEROTALES. II. THE BLEPHAROPLAST AND ANTERIOR MITOCHONDRION IN PHAEOCEROS LAEVIS: LATER DEVELOPMENT

Chromatin condensation begins as the multilayered structure (MLS) in Phaeoceros reaches its maximally structured differentiation. As nuclear elongation and chromatin condensation proceed, the S_2–4 strata disappear, and the nuclear beak extends between the S₁ and the nearly spherical anterior mitochondrion. In a mature sperm the mitochondrion is elongate and lies completely anterior to the blunt front end of the nucleus. The 12 S₁ tubules extend over the anterior mitochondrion and nucleus, but their number becomes reduced to five at the level where the nucleus' midportion is constricted. The anterior ends of the S₁ tubules lie embedded in a rather conical osmiophilic crest. Flagellar insertion is restricted to the extreme anterior tip of the S₁ tubules. The locomotory apparatus in Phaeoceros is compared with that of other bryophytes.