. Botany for high schools. Botany. 234 GENERAL MORPHOLOGY OF PLANTS often found floating on the water. Some of the cells in Anabcena become much longer than the others and larger. These function as spores and multiply the plant. 377. Review of the blue-green algae.—In addition to the characters and habits given under general char- acters it is to be noted that they differ from the other algae by the absence of sexual reproduction, or at least that sexuality has not yet been discovered in the group. THE DIATOMS (DIATOME.^: BACILLARIALES). 378. General characters.—The diatoms are single-celled p
. Botany for high schools. Botany. 234 GENERAL MORPHOLOGY OF PLANTS often found floating on the water. Some of the cells in Anabcena become much longer than the others and larger. These function as spores and multiply the plant. 377. Review of the blue-green algae.—In addition to the characters and habits given under general char- acters it is to be noted that they differ from the other algae by the absence of sexual reproduction, or at least that sexuality has not yet been discovered in the group. THE DIATOMS (DIATOME.^: BACILLARIALES). 378. General characters.—The diatoms are single-celled plants, a few remaining loosely joined into filaments. They are remarkable for the possession of a silicious skeleton, called a frustule, which encloses the protoplast. This skeleton is in two parts (valyes) resembling a box with its cover, some of the forms resembhng an old-fashioned pill box (fig. 194). Some of the frustules are remarkable for the fine and beautiful sculpturing, and are used for test objects in determining the resolving power of high-grade microscopic lenses. The diatoms occur in fresh and salt water. They exist in vast numbers. The diatoms together with other microscopic plants and animals form what is called the plankton (wandering life of the sea) of fresh and salt waters, especially of the deep waters. Extensive deposits of diatomaceous earth several feet in depth, made up almost entirely of the skeletons of diatoms, exist, for example, in southern England, in places in the Adirondack Mountains, at Richmond, Va., in Nevada, Cali- fornia, etc. This is sometimes used as a polishing powder. The frustules also occur in guano. 379. The frustules of the diatoms are of various forms, elliptical, oblong, wedge-shaped, circular, etc. Many are free,. Fig. 193. Nostoc linckii. A, filament with two heterocysts (//). and a large number of spores {sp)\ isolated spore beginning to germinate; C, young filament developed from spore. (After Bornet.). Please note that th
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