. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . arise singly or less often inpairs, and are furnished with either two or four cilia. In the large speciesU. zonata, in which zoogonidium-formation was very carefully studied byDodel (76), every gradation in size is met with between macrozoogonidia Ulotrichaceae 285 with four cilia and microzoogonidia with two cilia. Moreover, all thegradations of zoogonidia may be produced from the cells of the samefilament. In U. zonata 1C or 32 microzoogoni
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . arise singly or less often inpairs, and are furnished with either two or four cilia. In the large speciesU. zonata, in which zoogonidium-formation was very carefully studied byDodel (76), every gradation in size is met with between macrozoogonidia Ulotrichaceae 285 with four cilia and microzoogonidia with two cilia. Moreover, all thegradations of zoogonidia may be produced from the cells of the samefilament. In U. zonata 1C or 32 microzoogonidia are produced from eachmother-cell, but only 2 or 4 in U. subtilis; similarly, 2, 4 or 8 macro-zoogonidia (often complanate) are formed in U. zonata, but only one inU. &qnalis and U. subtilis. The zoogonidia germinate directly on comingto rest, and sometimes while still within the mother-cell (fig. 183 B and (7).Owing to the great variability in the size of the zoogonidia of U. zonata, thefilaments of this species vary greatly in thickness, but in other species ofthe genus there is a much greater uniformity in the thickness of Fig. 182. A—E, Ulothrix zonata (Web. & Mohr) Kiitz. A, formation of macrozoogonidia;B, macrozoogonidium showing 4 cilia, pigment-spot (st) and pyrenoids (py) ; C, formationof microzoogonidia; D, microzoogonidium ; E, escape of gametes, their conjugation (</),and the zygote some days after its formation (z). F, the zoogonidia of a form of U. tenerrimaKiitz. All x800. Gamogenesis takes place by the fusion of iso- or anisogametes. Thegametes are always biciliated, and in some species of Ulothrix and Sticho-coccus they are sufficiently differentiated in size to be termed macro- andmicrogametes. They may conjugate isogamously or anisogamously, orgerminate without conjugation (parthenogenetically). The gametes arefrequently quite indistinguishable from the microzoogonidia, a fact whichcauses one to suspect that the latter are facult
Size: 1827px × 1368px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishercambridgeengtheuni
