Spermatogenesis in Equisetum

In the early mitoses in the spermatogenous tissue of Equisetum there are no centrosomes, centrospheres, or asters. 2. A minute granule, surrounded by a weakly developed aster, appears in the cytoplasm near the nucleus in each of the cells of the penultimate generation. This granule divides to two, which become the blepharoplasts. 3. The two blepharoplasts, each with its aster, diverge to opposite poles of the nucleus. During the early stages of separation a distinct central spindle develops, so that an amphiaster is present. 4. The astral rays on the side toward the nucleus form two cones of fibers which, when the nuclear membrane breaks down, become the achromatic portion of the karyokinetic figure. The blepharoplasts occupy the poles. 5. During the anaphases and telophases of karyokinesis the blepharoplast enlarges, becomes vacuolate, and breaks up to a number of pieces. After further fragmentation these unite to form the cilia-bearing thread. 6. In the metamorphosis of the spermatid the nucleus and blepharoplast elongate spirally side by side, but have no connection other than that afforded by the undifferentiated cytoplasm. 7. The activities of the blepharoplast in Equisetum, taken together with the behavior of recognized true centrosomes in plants and analogous phenomena in animals, are believed to constitute conclusive evidence in favor of the theory that the blepharoplasts of bryophytes, pteridophytes, and gymnosperms are derived ontogenetically or phylogenetically from centrosomes.