THE FINE STRUCTURE OF OOGENESIS IN MARCHANTIA POLYMORPHA

Abstract

Archegonium development, beginning with the archegonial initial and culminating in the mature egg, was studied with the electron microscope. The ultrastructural features of the beginning stages in development of the archegonium are relatively similar to one another. Plasmodesmata occur between all adjacent cells at this time. After the secondary central cell is formed these protoplasmic connections are lost, and both axial and parietal cell lineages begin to show signs of ultrastructural differentiation. The mature egg is characterized by cytoplasm rich in ribosomes and larger organelles. Mitochondria and simplified plastids commonly display a juxtaposed association. As far as could be ascertained the numerous plastids and mitochondria in the egg of Marchantia arise through division of preexisting organelles and are not formed anew from evaginations of the nucleus. Blebbing of the nucleus produces polymorphic organelles which appear to be pinched off into the cytoplasm. The mature egg also contains vacuoles and lipid bodies toward its periphery, while dictyosomes and extensive endoplasmic reticulum occur throughout. The space between the wall cells and the mature egg appears to contain an amorphous substance. No extra membrane was observed around the mature egg.