Fungi, Ascomycetes, Ustilaginales, Uredinales . succeededin recognizing several separatechromosomes; a similar stateof affairs has been recorded byChristman for Phragmidiumspeciosum so that it would ap-pear that the different speciesof rusts are at dissimilar levelsin this matter, though a furtherstudy of carefully fixed materialmight be undertaken with ad-vantage. In all cases, however, thedivisions of the fusion nucleusof the teleutospore are muchmore elaborate than those in thevegetative cells and show someof the characteristics of a meioticIn Coleosporium (fig. 189) the fusion nucleus at f
Fungi, Ascomycetes, Ustilaginales, Uredinales . succeededin recognizing several separatechromosomes; a similar stateof affairs has been recorded byChristman for Phragmidiumspeciosum so that it would ap-pear that the different speciesof rusts are at dissimilar levelsin this matter, though a furtherstudy of carefully fixed materialmight be undertaken with ad-vantage. In all cases, however, thedivisions of the fusion nucleusof the teleutospore are muchmore elaborate than those in thevegetative cells and show someof the characteristics of a meioticIn Coleosporium (fig. 189) the fusion nucleus at first possesses awell-marked reticulum of interlacing threads. This undergoes a stage ofconcentration in one part of the nuclear area, which no doubt correspondsto synapsis, and afterwards loosens out, increases in thickness and forms aspireme. The spireme breaks up and its segments are seen to be doublethroughout their length. In the meantime centrosomes and spindle fibreshave appeared and characteristic gemini are recognizable on the Coleosporium Senecionis; mitosis in teleuto-spores; after Arnaud. phase. VIII] URKDINALKS 213 Moreau describes only two, but I [arper and 1 [olden found a larger number,which became crowded together and more or less fused during the laterstages of the first and also during the second division. In Gymnosporangium clavariaeforme (fig. 190) the first divisii >n is initiated,as in Coleosporium, by a synaptic phase, after which a spireme is formed andbreaks up into chromosomes. These pass on to the spindle M /. \??.. ,y but soon lose their individuality \and travel in irregular massesto the poles. The development of thespindle has also been traced inthis species ; its formation isextra-nuclear and it lies free inthe cytoplasm before cominginto relation with the dividingnucleus. This type is fairlycommon among animals but isof exceptional occurrence inplants. Nuclear Association. Thecytology of the aecidium wasfirst described in detail in 1
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectfungi, bookyear1922
