. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. 64 PLECTOMYCETES [CH. structure, the ascus. The fusion nucleus divides to form four or eight daughter nuclei about which ascospores are organized (fig. 25). Sometimes the limits of the conjugating cells can be distinguished after the ascospores are formed, two or four lying in each of the original cells. In the closely related Sch. Pombe and Sch. fnel- lacei copulation takes place in a very similar way, but the union of the conjugating. Fig. 25. Schizosacckaromyces octosponis Beyrinck; conjuga- tion and formation of ascospores; after Guil
. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. 64 PLECTOMYCETES [CH. structure, the ascus. The fusion nucleus divides to form four or eight daughter nuclei about which ascospores are organized (fig. 25). Sometimes the limits of the conjugating cells can be distinguished after the ascospores are formed, two or four lying in each of the original cells. In the closely related Sch. Pombe and Sch. fnel- lacei copulation takes place in a very similar way, but the union of the conjugating. Fig. 25. Schizosacckaromyces octosponis Beyrinck; conjuga- tion and formation of ascospores; after Guilliermond. cells is less complete than is usually the case in Sch. octosporus, and the number of ascospores is regularly four. The mature ascus is thus dumb-bell shaped, with two spoi^es in each enlargement. Also in 1901 Barker discovered the yeast Zygosaccharomyces Barkeri and observed in it a conjugation similar to that of Sch. Pombe. Following on these observations a number of other cases of conjugation among the yeasts have been recognized. Many species form two spores, one at each end of a dumb-bell shaped ascus; in others a single spore is produced, the fusion nucleus passing from the conjugation tube into one of the fusion cells, while the other remains empty. Such cases lead up to the state of affairs in Zygosaccharomyces Chevalieri where conjugation is between two cells of different sizes, the whole contents of the smaller passing into the larger cell which is then cut off by a wall. In the larger cell nuclear fusion takes place and one to four ascospores are formed. In Gtiilliennondia fulvescens conjugation is between a mature cell and its bud. The whole contents of the bud pass back into the parent cell, nuclear fusion takes place and a fresh bud is put out in which the single ascospore develops. It has been suggested that this represents a rudimentary sporo- phyte. The problems connected with meiosis hardly arise here if, as Wager has shown for Saccharomyces, amitosi
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectfungi, bookyear1922
