The Ascogenous Hyphae of Pyronema confluens1

Abstract

The ascogenous hyphae arise from the oogonium, opposite groups of nuclei, as minute, enucleate papillae. Nuclei pass into them singly, rarely two at a time, and a knob-like swelling is formed, containing several nuclei and later growing out into one or more branches. The nuclei are in single file in the branches and irregularly arranged in the bulbous base. There are frequently two nuclei in a leading position at the tip of the young branch, but the nuclei may become more evenly spaced as the hypha elongates. The nuclei undergo a simultaneous mitosis. The spindles of the dividing nuclei in the branches are not parallel and this is, therefore, not a conjugate division. Walls are formed as ingrowing rings across the spindles so that the ascogenous hypha, when septate, has a uninucleate end cell followed by one, or usually more, binucleate cells and a basal bulb containing a variable number of nuclei. Croziers are formed as lateral, hooked outgrowths from the binucleate cells. After a simultaneous mitosis of the two nuclei a uninucleate end cell, a binucleate penultimate cell, and a uninucleate stalk cell are formed. Thus, the division in the crozier and that in the ascogenous hypha are alike. The binucleate cell of the crozier may proliferate to form another crozier, or it may form an ascus after the fusion of its two nuclei. The stalk and terminal cell of the crozier may anastomose and grow out to form a lateral crozier. The chromosome number in the mitosis in the ascogenous hypha is twelve and there are twelve bivalents at the first division of meiosis in the ascus. The effect of increasing the illumination of the cultures with an electric lamp in addition to diffuse daylight is to ensure the further development of all early formed sexual organs, to make the ascogenous hyphae develop rapidly, to make the latter short and curved in form with few binucleate cells, and to increase the tendency towards a period of erect proliferation before the formation of the asci and lateral proliferation begin. The bearing of the results on current theories of sexuality in the Ascomycetes is discussed.