Studies on Ascoidea Rubescens—II Cytological Observations

SUMMARY

1.	For these studies materials collected at Ithaca, New York, in August, 1927, and at Lincoln, Nebraska, in June, 1930–1933, inclusive, were used.
2.	The hyphae, conidia, and spore sacs are coenocytic but the spores formed in the spore sac are uninucleate.
3.	The nuclei are much larger in young cells than older cells but all are similar in structure and are characterized by a large nucleolus and little additional chromatic material.
4.	Characteristic chromatic bodies of several types are conspicuously present in coenocytic cells. Some of these at least arise from degenerated nuclei. The most conspicuous of these is a granular disk to which a homogeneous highly refractive globule is centrally attached. These are evidently the bodies considered specialized nuclei by Varitchak.
5.	Active growth is apical; new cells are formed as soon as the apical cell has elongated so as to be about a third longer than a typical cell. Cells below the apical region have scanty protoplasm and older cells lose their protoplasmic content.
6.	All reproductive structures on actively growing thalli are apical, the surface of the thallus often appearing like a vague hymenium.
7.	Hyphal tips contain up to 20 or more nuclei, young spore sacs up to 40 nuclei, and mature spore sacs up to 160 spores.
8.	The nuclei for the spores formed in spore sacs arise by simultaneous divisions.
9.	Spores are first differentiated in spore sacs as lens-shaped masses of denser protoplasm, flattened on one surface and rounded on the other, and are surrounded by less dense cytoplasm.
10.	The characteristic hat-shape of the endogenously developed spores is due to the fact that the wall of the spore is formed next to the dense cytoplasm of the spore initial on its flat surface and on the outside of a clear layer of gelatinous appearance over the rounded surface. As the gelatinous layer disappears the “brim” of the “ hat “ is formed where these walls unite.
11.	The spores formed in spore sacs enlarge and become two to several nucleate before forming germ tubes. They give rise to coenocytic hyphae either directly or after fusions.
12.	Conidia of all types are multinucleate. They give rise either to conidia by budding or to coenocytic hyphae.
13.	Nuclear divisions in the sporangium are probably mitotic, and probable stages are discussed. Similar figures were occasionally observed in vegetative cells. There are also some indications of amitosis.
14.	The spore sac is probably an apogamously developed ascus.
15.	These studies indicate that Ascoidea is a true Hemiascaceous fungus closely related to Dipodascus and Endomyces. The term hemiascus can well be applied to such asci.

The writer wishes to extend thanks to Prof. H. M. Fitzpatrick, of Cornell University, for his continued interest, and for suggestions made during the progress of these studies and after reading a first draft of this paper; to the Michigan Biological Station for laboratory facilities and courtesies during the summer of 1930; and to T. J. Fitzpatrick for editing and proof reading the paper.