National Geographic : 1961 Feb
National Geographic, February, 1961 are the trappers of solar energy, the creators of the basic bread of the oceans. Each diatom, a tiny one-celled plant, has a shell of silica-the main ingredient of sand and glass. The shell consists of transparent halves, one fitting inside the other just as the bottom of a pillbox fits inside the top. Indeed, some species are box shaped; others are like spindles or wedges of pie. Diatoms reproduce by dividing. The over lapping halves separate, each with a new shell secreted to fit inside the old. Thus the offspring developing from the "box bottom" is always smaller than its parent, and the size keeps dwindling through successive genera tions. Finally, one sends out a reproductive mass within which new cases form to the species' original measurement, and the whole process starts again. The diatoms multiply prodigiously. One diatom may have 100 million descendants in 30 days. And it is well that they are so pro lific, for a single copepod may consume more than 120,000 diatoms in a day. And the num- ber of copepods in the sea may exceed the total of all the other multicellular animals of the earth. Undigested silica shells of diatoms, and cases of those that die, sink to the bottom and form layers of siliceous ooze. Upheavals of ancient sea bottoms have exposed deposits of such diatomaceous earth as much as 1,400 feet thick. Each cubic inch of these deposits contains the shells of perhaps 50 million dia toms! Man mines this earth in huge quanti ties for a wide variety of uses (page 209). Scientists have found that the protein and fat content of diatoms is about the same as that of average meadow hay. They have dis covered also that the oil droplets frequently locked in the diatoms' silica cases are rich in vitamins. The stores of vitamins A and D we extract from the livers of fish had their origin in diatoms and other lowly marine plants the fish fed upon. In my microscope I could see an occasional speck of oil within the glassy shells. But most conspicuous in the diatoms' insides were ir regularly shaped masses of chloro- KODACHROMEBY NATIONAL GEOGRAPHICPHOTOGRAPHERTHOMASJ. ABERCROMBIE© N.G.S. phyll- at times a bright green, more often made earth color by the masking effect of a brown pigment (page 208). Hues of diatoms range from browns through olive green to canary. The sulphur-bottom whale gets its name from yellow diatoms that grow in pro fusion on its belly. Each diatom is a simple single-celled organism. Yet in its primitive proto plasm a process takes place that man, the great chemist and engineer, has not yet managed to duplicate. That process is photosynthesis. We know what happens in photo Model of a complex molecule shows how nature binds 137 atoms to create chlorophyll. At the core of the model, 380 million times actual size, lies a single magnesium atom (green). Fifty-five carbon atoms (black), 72 hydrogen (white), 5 oxy gen (red), and 4 nitrogen (orange) cluster around it. Some balls hide others in this view. Prof. Robert Burns Woodward, shown in his Harvard laboratory, recently syn thesized chlorophyll. His achieve ment proves chemists' theories a bout the compound's structure and gives them new tools to unlock secrets of other complex molecules.