. Text-book of botany, morphological and physiological. Botany. ZYGOSPORES. 255 disappear. Some minutes after the commencement of conjugation the resulting zygospore is a spherical cell (VI), which remains at rest for some time enclosed in its cell-wall, its green colour passing over into a brick-red. If the dried-up zygospores, which have now greatly increased in size, are placed in water, germination begins after twenty-four hours; the outer shell of the cell-wall breaks up, an inner membrane protrudes and now contains one, two, or three large zoospores which finally escape (nil, IX), surrou
. Text-book of botany, morphological and physiological. Botany. ZYGOSPORES. 255 disappear. Some minutes after the commencement of conjugation the resulting zygospore is a spherical cell (VI), which remains at rest for some time enclosed in its cell-wall, its green colour passing over into a brick-red. If the dried-up zygospores, which have now greatly increased in size, are placed in water, germination begins after twenty-four hours; the outer shell of the cell-wall breaks up, an inner membrane protrudes and now contains one, two, or three large zoospores which finally escape (nil, IX), surround themselves, after a short period of swarming, with a gelatinous envelope, and break up by successive divisions into sixteen primordial cells which now again form a coenobium like Fig. 1. A further illustration of the course of development in the Pandorineae is furnished by Stephanosphmra plwvialis, one of the rarest and most beautiful of the family (Fig. 168), occurring rarely in the rain-water which collects in the hollow of large stones. The process of vegetative reproduction is the same as in Pandorina; but, according to Cohn and Wichura, the succession of generations of this kind is interrupted by the cells belonging to a family dividing repeatedly (Fig. 168, XII) into zoogonidia which ultimately become free (XIII), and probably produce resting zygospores by. FIG. 168.—Successive stages in the reproduction of Stephanosphcera phivialis (after Cohn and Wichura). conjugation after the manner of Pandorina. It is stated by the observers above-named that stationary immotile balls (I) accumulate at the bottom of the water which, as they grow, assume a red colour. After these resting-cells, which are probably zygospores, have lain for some time dry and then again been moistened, they germinate, the contents breaking up into from 4 to 8 zoospores (II—V) which invest themselves with a cell- wall, and each gives rise, in a single day by successive division (VII—IX), to an eig
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
