. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. DIATOMS 207 of almost pure silica slowly accumulate at the bottom of the water. Instances are afforded by the extensive beds of " dia- tomaceous earth " found at DolgeUy in Wales, at Bihn in Bohemia, and elsewhere, some being of marine, others of freshwater origin. Such deposits are utilised commercially in the preparation of dentifrices and, owing to the very small size of the individual particles, for mixing with nitroglycerine in the manufacture of dynamite. The extensive vegetable Plankton of th
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. DIATOMS 207 of almost pure silica slowly accumulate at the bottom of the water. Instances are afforded by the extensive beds of " dia- tomaceous earth " found at DolgeUy in Wales, at Bihn in Bohemia, and elsewhere, some being of marine, others of freshwater origin. Such deposits are utilised commercially in the preparation of dentifrices and, owing to the very small size of the individual particles, for mixing with nitroglycerine in the manufacture of dynamite. The extensive vegetable Plankton of the sea at times consists almost entirely of Diatoms. Although several groups of Algae are designated ac- cording to the prevailing colour of their chloroplasts, they are characterised by many more important features, and especially by the nature of their repro- ductive processes (see next chapter). The chloroplasts, in general, assume the most complex forms among the Green Alga, where there is often but a single one in each cell, a condition al- ready noticed in Chlamy- domonas and its aUies (cf. p. 181). Moreover, the chloroplasts of the Green Algse commonly possess one or more pyrenoids and, during active assimilation, starch is formed as a reserve-product, first around the pyrenoids, and then in the general substance of the plastid. Whilst most of the colonial [ Scenedesvius) and less differ- entiated filamentous forms [ Ulothrix) have a relatively simple undivided chloroplast, greater complexity is met with in many of the more highly organised Green Algae. The chloroplast of Ulothrix is a curved band having the form of an incomplete cylinder (Fig. 115, a, c), which occupies the. Fig. 113.—Various Diatoms (only the siliceous shells are shown), a and c, Navicula ; b, Nitzschia ; d, Cym- hella ; e, end-view, and /, side-view of cells of the colonial Please note that these images are extracted from scanned page images that may have been digitally enhanced fo
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