Cell Relations in the Perithecium of Ceratostomella Multiannulata

SUMMARY

The development of the ascogenous system in the perithecium of Ceratostomella multiannulata follows the fragmentation of an originally binucleate unwalled ascogonium. The first division of the ascogonium is indirect and results in the formation of two uninucleate fragments and a single binucleate cell. The binucleate or fertile portion of the ascogonium undergoes a linear growth accompanied by conjugate nuclear divisions. At approximately the 8-nucleate stage, the fertile coil divides into independent units of 2 or 4 nuclei each. Each unit continues to divide independently. The uninucleate fragments resulting from the first division of the ascogonium undergo an independent proliferation within the perithecial cavity and give origin to a layer of space-making cells that at one stage surrounds the group of binucleate protoplasts. The uninucleate or space-making cells later collect at the base of the perithecial cavity where they dwindle in number and disappear before the perithecium reaches maturity.

Successive divisions of the binucleate fragments of the ascogonium result in the formation of a multitude of minute, independent and unwalled cells that later develop into asci. Stages in division of the ascogenous cells include the crosier as well as several other, both direct and indirect, types of cell cleavage. Cell divisions are accompanied by significant changes in cell shape. Short chains or independent groups of cells constitute the only suggestions of hyphal growths to be observed in the perithecium. Developing asci are frequently linked together in short series, while actively dividing cells are mostly unattached.

Actively dividing cells in an advanced perithecium cover the lower face of the perithecial cavity and appear to consume the pseudoparenchyma of thin-walled cells lining the interior. The “space-making” function, therefore, does not appear to be restricted to the system of uninucleate cells that is present in the perithecium at an early stage of development.

The asci are unwalled. Ascospore formation is restricted to a central region of the ascus cytoplasm which, however, is not clearly vesiculate. Immature ascospores appear to be attached at a common base which is usually lateral to the longer dimension of the ascus. Deliquescence of the ascus involves a dissolution of the peripheral layer of cytoplasm and a separation of the closely compact group of 8 spores.