. Principles of modern biology. Biology. 598 - Heredity and Evolution. Fig. 31-3. One of the golden-brown algae (Chrysophyta), the diatom, Pinnularia. Note the finely etched, glassy cell wall and the overlapping halves of the "; These features are common to all diatoms. (From The Plant World, by Fuller and Carothers. Holt, Rinehart and Winston, Inc.) is formed like a medicinal capsule—with tu<o symmetrical slightly overlapping halves (Fig. 31-3). Moreover, the capsule is finely etched with dots and markings of such ex- quisite delicacy that diatoms are often used by micros
. Principles of modern biology. Biology. 598 - Heredity and Evolution. Fig. 31-3. One of the golden-brown algae (Chrysophyta), the diatom, Pinnularia. Note the finely etched, glassy cell wall and the overlapping halves of the "; These features are common to all diatoms. (From The Plant World, by Fuller and Carothers. Holt, Rinehart and Winston, Inc.) is formed like a medicinal capsule—with tu<o symmetrical slightly overlapping halves (Fig. 31-3). Moreover, the capsule is finely etched with dots and markings of such ex- quisite delicacy that diatoms are often used by microscopists for testing the resolving power of high quality lenses. Typical nuclei and chloroplasts are pres- ent (Fig. 31-3). However, in addition to chlorophyll, the chrysophytes possess a brown pigment, fucoxanthin, which is likewise found in the brown algae (p. 599) and in the (lame algae (p. 598). The intracellular storage product is a fluid lipid, generally re- ferred to as oil, rather than solid granules of a carbohydrate nature. Diatoms occur in enormous abundance and variety in most salt and fresh waters. A cubic loot of ocean water frequently will contain well over a million specimens. In fact, the diatoms, together with the dinofla- gellates (p. 599), are sometimes referred to as the "grass of the sea," because they repre- sent such an important food base for fish and other marine animals. By dint of num- bers these organisms appear to be responsible directly and indirectly for the synthesis of considerably more than half of all existing organic matter (p. 158). And in past ages, extending back into the early Paleozoic era, diatoms nourished in equal if not greater abundance. Some sedimentary deposits of diatomaceous earth, which consists largely of the distinctively marked, silicon-laden cap- sules of ancient diatoms, display a depth greater than 1000 feet. This material, be- cause of its exceedingly fine abrasive quali- ties, is used extensively in the prep
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