Ultrastructure of the germinating spores of Physarella oblonga f. alba

Observations by transmission electron microscopy of germinating Physarella oblonga f. alba spores show a densely fibrous zone from which is excluded all structural components at the site of emergence. Early in germination structural breakdown of the wall occurs along with an extension of the intervening space from spore wall to the plasma membrane. Both wall changes and the fibrous emergence zone may represent sites of internal enzymatic activity. Unique structural features include the development of digestive vacuoles prior to spore germination, small electron dense bodies in cytoplasmic vesicles and the wall zone, binucleate spores, and membrane-limited bodies appearing as doughnut-shaped or circular structures.