. The essentials of botany. Botany. DESMIDS 179 family (Closteriaceae) the elongated cylindrical cells sepa- rate early and become more or less attenuated, as in Closterium. In a third family {Cosma- riaceae) the flattened, more or less con- stricted cells separate very early, and in many cases become terminally much lobed or otherwise modified. Of the less modified desmids the species of —Desmids: ^^ . , 1 1 •! Closterium, Cosma- Cosmarmm are good examples, while rium, and Micra- those of Euastrum and Micrasterias are greatly modified, the cells of the latter being divided into many po
. The essentials of botany. Botany. DESMIDS 179 family (Closteriaceae) the elongated cylindrical cells sepa- rate early and become more or less attenuated, as in Closterium. In a third family {Cosma- riaceae) the flattened, more or less con- stricted cells separate very early, and in many cases become terminally much lobed or otherwise modified. Of the less modified desmids the species of —Desmids: ^^ . , 1 1 •! Closterium, Cosma- Cosmarmm are good examples, while rium, and Micra- those of Euastrum and Micrasterias are greatly modified, the cells of the latter being divided into many pointed lobes. 254. In generation the desmid cells break open at the middle (where there is commonly a joint in the wall) and the two protoplasms (isogametes) unite into a zygote, which eventually becomes a thick-walled resting spore. After some time the resting spore germinates by ruptur- ing its wall and dividing the contents into two, four or eight new non-ciliated cells which eventually become like the parent cells. 255. Desmids are fresh-water plants, floating free in the waters of quiet pools, or entangled with mosses or other aquatic plants. Class 6. BACILLARIOIDEAE 256. The plants of this class are the Diatoms, num- bering about 5700 species, or even as many as 10,000 species in the opinion of some botanists. Some diatoms are filamentous, but in the greater number the filaments fragment early into single cells. The cells contain chlorophyll, which is commonly hidden by the addition of diatomin, a yellow-brown pigment. A few diatoms are colorless, and hysterophyliic, and therefore are ";. 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 Bessey, Charles E. (Charles Edwin), 1845-1915; Bessey, Ernst Athearn, 1877-1957. joint author. New York, H. Holt and company
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