. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. Ill ASCOMYCETES 45 was proposed. The occurrence of a brachymeiotic reduction has since been observed in several other fungi, and has also been in several cases denied. Chromosome Association. There are a number of fungi, of which Phyllactinia Corylea is perhaps the most fully studied, in which no change in the chromosome number takes place throughout the life-history. In Phyl- lactinia, Harper showed in 1905 that the chromosomes remain visible in strands attached to the central body throughout the resting stages. In each of the nuclei of
. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. Ill ASCOMYCETES 45 was proposed. The occurrence of a brachymeiotic reduction has since been observed in several other fungi, and has also been in several cases denied. Chromosome Association. There are a number of fungi, of which Phyllactinia Corylea is perhaps the most fully studied, in which no change in the chromosome number takes place throughout the life-history. In Phyl- lactinia, Harper showed in 1905 that the chromosomes remain visible in strands attached to the central body throughout the resting stages. In each of the nuclei of the developing ascus eight such strands can be clearly seen (fig. 14), and their asso- ciation in pairs can be followed, so that they appear as eight strands in the spireme stage, and as eight chromosomes on the spindle. In the smaller sexual nuclei Harper found a similar arrangement. It would thus appear that in this fungus chro- mosome association follows directly on nuclear fusion, so that the fusion of two nuclei with n univalentstrands produces not a nucleus with 2n. Fig. 14. Phyllactinia Corylea (Pers.) Karsl.; fusion nuclei in ascus showing eight chromatin strands attached at a common point; after Harper. Strands, but one with n bivalent strands. If this is so in the oogonium the nuclei which fuse in the ascus will each possess n bivalent chromosomes, and the definitive nucleus will show not 4% univalent chromosomes but n which are quadrivalent. In the same way neither meiosis nor brachymeiosis will affect the chromosome number, but will affect only the valency of the chromosomes. This is the case in Phyllactinia, where in all stages of the three divisions in the ascus, eight chromosomes are found. It must be noted, however, that in cases where no fusion occurred in the life-history except that which immediately precedes meiosis, the chromosome number would similarly remain unchanged; the latter interpretation has been urged as evidence that forms in which the chromosome
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectfungi, bookyear1922
