The ultrastructure of oogenesis in the fern
Osmunda cinnamomea
L. var.
asiatica Fernald has been studied by electron microscopy. During oogenesis, numerous vesicles not only moved towards the periphery, but also were arranged in line along the inside of plasmalemma, and in addition aggregated outside the plasmalemma by exocytosis. They released or excreted osmiophilic material. It was observed that a few vesicles containinglamellar osmiophilic materialsituated closely along the plasmalemma, seemed to break open. Simultaneously, a separation cavity between egg cell andarchegonium wallformed.Its width was broader than the other advanced ferns reported previously, and an extra egg membrane occurred outside around the plasmalemma of the egg, its thickness being greater than in
Pteridium
and
Dryopteris
. Amyloplasts around the nucleus were filled withlarge triangular semicircular or subelliptical starch grains, but as the egg matured they progressively decreased. Nucleus was large and flattened, and paired membrane in two to three couples laid within the nucleus, close and parallel to the nuclear membrane. No nuclear evagination was observed. Mitochondria seemed to have been undeveloped, but finally recovered normally.
