192 SECTIONAL ADDRESSES. 



ASCOMYCETES. 



In the Ascomycetes the sexual apparatus has in many cases been shown 

 to be functional, with well differentiated male and female organs. In the 

 simpler species, among the Plectascales, the gametangia are similar twisted 

 filaments ; in Eremascus albus these fuse,^^ the contents of both passing 

 into an enlargement which becomes the ascus directly and gives rise 

 internally to eight spores. In Endomyces Magnusii^'^ the gametangia 

 differ in size, the contents of the smaller passing into the larger which 

 becomes the ascus. In Endomyces Lindneri^^ the product of fusion is not 

 an ascus, but buds out one or two short hyphse at the end of each of which 

 an ascus is developed. Here we have the beginning of the vegetative 

 sporophyte which, in the higher Ascomycetes, forms a considerable mass 

 of ascogenous filaments bearing numerous eight-spored asci. In the first 

 two divisions of the nucleus of the ascus meiosis occurs, and the ascospores 

 give rise, on germination, to the vegetative gametophyte. I do not 

 propose to discuss the complicated cytology of this stage, but to accept, 

 for my present purpose, the common ground that, in some cases at any 

 rate, male nuclei enter the oogonium and sooner or later fuse with the 

 female nuclei ; while, in other species, or in the same species under 

 different conditions, more or less marked apogamy prevails, so that the 

 antheridium may be functionless or missing, the oogonium still giving 

 rise to ascogenous hyphse, or the female apparatus also may have dis- 

 appeared, the sporophyte being vegetative in origin. 



Proceeding from the simple, intertwined gametangia, we may recognise 

 a number of forms in which the female apparatus, or archicarp, is differ- 

 entiated into three parts, a stalk, commonly multicellular, an oogonium, 

 which may or may not become septate after the fertilisation stage, and a 

 trichogyne or conjugation tube, which also, strangely enough, is often 

 septate, the septa, at any rate in some cases,^^ having been shown to 

 undergo perforation. Evolution seems to have been along two lines : in 

 one, characteristic of the Pyrenomycetes, the archicarp remains narrow 

 and elongated, and septation is increased ; in the other, common among 

 Discomycetes, the oogonium is globose and septa are not developed. 

 This type is admirably exemplified by that classical subject of 

 investigation, Pyronema confluens. 



Corresponding to the discomycetous type of archicarp, we find a rather 

 large, stalked, oblong antheridium ; while, in the higher Pyrenomycetes, 

 the antheridium is reduced in size, and at last appears as a small, uni- 

 nucleate cell, detached from the end of an antheridial hypha. Such 

 antheridia have never been proved to function, and have by many been 

 described as conidia. Craigie's work on the spermatia of rusts indicates 

 the need of a reinvestigation of such forms. 



In both Pyrenomycetes and Discomycetes dioecious species have been 

 reported. Thaxter,^' in 1896, described the development side by side of 

 male and female plants of the laboulbeniaceous fungus, Amorphomyces 

 FalagricB ; in this species the ascus contains spores of two sizes, and these 

 male and female producing spores are shed in pairs. It is one of the 

 puzzling aspects, not merely of the fungi, but of plant economy as a whole, 

 that elaborate morphological provision for exogamy seems so often to be 

 neutralised by the common origin of the sexual elements or of the plants 



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