Light- and electron-microscopic studies of growth and reproduction inCutleria (Phaeophyta)

Summary Differentiation of the female gametangium inCutleria bancockii Dawson is described. Four series of mitoses result in a 16-locule structure (four tiers of four cells each). The organelles in each locule become polarized after partitioning is complete, with the mitochondria lying near the longitudinal axis of the gametangium. The nucleus and plastids are centrally located, with abundant osmiophilic material present in the cytoplasm subjacent to the gametangial surface. Both electron density and Toluidine Blue 0 staining of the material increase. Two flagella are then produced: one becomes tightly appressed to the plasmalemma near its base, and the other is free. A prominent eyespot forms in the plastid nearest the developing flagella. Golgi and endoplasmic reticulum vesicles are prolific in this region and seem to be involved with mastigoneme production and deposition on the free flagellum. Immediately beneath the plasmalemma, flagellar rootlet tubules emanate from amorphous masses near the basal bodies. Some of these tubules are associated with the eyespot. Most of the osmiophilic material is then secreted into the extracytoplasmic spaces while the gametes are rounding up. Granular-cored vesicles may be involved with pore formation and gamete release.