. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. n] ASCOMYCETES 47 four. Further the adhesion of chromosomes already described for Phyllac- tinia must not be forgotten. The occurrence of paired nuclei in the ascogenous hyphae was thus the most important evidence in favour of Claussen's view until in 1916 Welsford showed that the nuclei even of gametophytic, multinucleate hyphae are habitually paired if rapid growth and division are taking place; this is due to the fact that mitoses follow one another so rapidly that the daughter nuclei of any parti- cular division have not time to move
. Fungi, ascomycetes, ustilaginales, uredinales. Fungi. n] ASCOMYCETES 47 four. Further the adhesion of chromosomes already described for Phyllac- tinia must not be forgotten. The occurrence of paired nuclei in the ascogenous hyphae was thus the most important evidence in favour of Claussen's view until in 1916 Welsford showed that the nuclei even of gametophytic, multinucleate hyphae are habitually paired if rapid growth and division are taking place; this is due to the fact that mitoses follow one another so rapidly that the daughter nuclei of any parti- cular division have not time to move apart, before they them- selves divide. Such paired nu- clei have often previously been figured though without attract- ing special attention; excellent examples are to be seen in Nichols' paper on the Pyreno- mycetes' or in Ramlow's more recent work on Ascophanus car- neus"^. It seems hardly possible to place a different interpreta- tion on the nuclei which lie close together in the ascoge- nous hyphae. According to our present knowledge of the cytology of the Ascomycetes there are two nuclear fusions in the life- history of these plants. The Significance of the Fusion in the Ascus. If this be the case it remains to consider the significance of the fusion in the ascus. The presence of more than one nucleus in this cell, destined to be one of the largest in the life-cycle of the fungus, is hardly surprising especially in coenocytic forms. In uninucleate species it forms part, as Harper pointed out in 1905, â of the quantitative adjustment frequently observed between cytoplasm and nuclear material. But this nucleo-cytoplasmic relation does not explain why fusion should take place between the nuclei concerned or why they should be regularly two in number^ It is possible that, crowded as they are in the â newly constituted ascus, the nuclei merely flow together as they make ready for the prophases of division. Whatever may have been the determining 1 Bot. Gas. 1896, xxii, p
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