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The desmids, members of Chlorophyta, have flattened, relatively large Cells, with a characteristic bilateral symmetry (Figure 26.4). Asexual reproduction involves the systhesis of two new half-Cells in the equitorial plane, followed by cleavage between the new half-Cells to produce two bilaterally symmetrical daughters, each of which has a Cell consisting of an"old" and a "new" half.
 
The desmids, members of Chlorophyta, have flattened, relatively large Cells, with a characteristic bilateral symmetry (Figure 26.4). Asexual reproduction involves the systhesis of two new half-Cells in the equitorial plane, followed by cleavage between the new half-Cells to produce two bilaterally symmetrical daughters, each of which has a Cell consisting of an"old" and a "new" half.
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The diatoms (Figure 26.5), members of the Chrysophyta, have organic walls impregnated with silica. The architecture of the diatom wall is exceedingly complex; it always consists of two overlapping halves,like the halves of apetri dish. Division is longitudinal , each daughter Cell retaining half of the old wall and synthesizing a new half.
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The diatoms (Figure 26.5), members of the Chrysophyta, have organic walls impregnated with silica. The architecture of the diatom wall is exceedingly complex; it always consists of two overlapping halves, like the halves of a petri dish. Division is longitudinal, each daughter Cell retaining half of the old wall and synthesizing a new half.
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Although devoid of flagella, some desmids and diatoms can move slowly over solid substrates. The mechanism of desmid locomotion is not known. The locomotion of diatoms is accomplished by a special modification of ameboid movement. In
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Although devoid of flagella, some desmids and diatoms can move slowly over solid substrates. The mechanism of desmid locomotion is not known. The locomotion of diatoms is accomplished by a special modification of ameboid movement. In motile diatoms, there is a narrow longitudinal slot in the wall, known as a ''raphe'', through which the protoplast canmake direct contact with the substrate. Movement is brought about by directed cytoplasmic streaming in he canal of the raphe, which pushes the Cell over the substrate.
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Many fossil diatoms are known
    
== The Natural Distribution of Algae ==
 
== The Natural Distribution of Algae ==
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