. Lectures on the evolution of plants. Botany; Plants. 52 EVOLUTION OF PLANTS. the filament shows a distinction between base and apex. The most specialized forms, Coleochsete (Fig. 10), have the form of a flattened disk, and recall somewhat the structure found in the simplest mosses. Within the Confer- vacesB there is found a similar advance in the reproductive parts to that described in the Volvocinese. Some of the lowest forms have as yet shown only non-sex- ual reproductive cells, but it is not improbable that sexuality will be shown for all of them. In these forms where only non-sexua
. Lectures on the evolution of plants. Botany; Plants. 52 EVOLUTION OF PLANTS. the filament shows a distinction between base and apex. The most specialized forms, Coleochsete (Fig. 10), have the form of a flattened disk, and recall somewhat the structure found in the simplest mosses. Within the Confer- vacesB there is found a similar advance in the reproductive parts to that described in the Volvocinese. Some of the lowest forms have as yet shown only non-sex- ual reproductive cells, but it is not improbable that sexuality will be shown for all of them. In these forms where only non-sexual zo- ospores have been ob- served, they may be either uniciliate or biciliate. These zoospores may arise singly, by the escape of the whole of the contents of a cell as a single zoospore; or there may be a division of the cell-contents into two or more parts which then escape. When the zoospores are large (Fig. 9, D), they sometimes have more than two cilia, but otherwise resemble closely the typical Volvox cell. The simplest type of sexual reproduction among the Confervacese consists in the formation of cells (gametes), which differ from the zoospores only in being, as a rule, smaller, but with no distinction of sex. These gametes ZBt. Fig. 8 (Confervacese). — A, a filament of Microspora, composed of entirely uniform cells; B, part of a plant of Cladophora, showing the branching hahit; C, a zoospore of Cladophora, showing the two cilia, the eye-spot, e, and the nucleus, n; D, gametes, or sexual cells, of Ulothrix, showing the process of conjugation. (, after Dodel.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Campbell, Douglas Houghton, 1859-1953. New York, The Macmillan Co. , London, Macmillan & Co. , Ltd.
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Keywords: ., bookcentury1800, bookdecade, booksubjectbotany, booksubjectplants
