National Geographic : 1934 Jun
THE NATIONAL GEOGRAPHIC MAGAZINE her and we turn toward the wonderful ex panse of the reef at the base of which we are standing and begin our observations. PAINTING OIL COLORS UNDER SEA Chris Olsen, my chief artist and modeler, ingenious and resourceful, was with me on three of my expeditions and was always my right-hand man. On our most recent trip he was prepared with Monel metal easel and palette, which he had contrived for the pur pose, and stood 20 feet below the surface in his diving helmet, sketching the coral reef from Nature with oil colors on a specially prepared canvas stretched over plate glass and framed in his non-corrosive easel. At first he used paint brushes with wooden handles. Once he forgot and tried to set one down. It immediately floated to the surface and we had to send out a man in a rowboat to get it. I brought it back to him, using a diving helmet for the purpose. After that he used a palette knife, which would not float and also was much handier for laying on colors under sea. The undersea gardens were a perpetual wonder to us. It was hard to realize, as we gazed through the windows of our diving helmets at the towering pinnacles of the reef, and clambered in half-floating leaps over the rounded heads of massive coral that rose in terraces to the water surface, that these huge castellated structures were erected through the vital energy of such delicate coral polyps. Yet there they were by the millions, covering every square inch of the growing coral (see Color Plate IV). In the mellow light of the more protected areas, their serried communities expanded with outreaching, feathery tentacles sur rounding their miniature mouth slits-veri table petals of animal flowers (see Color Plate III). In patches of stronger sunlight, whole phalanxes were flattened to a mere investment of the underlying hard parts with thin gossamer films of living tissue, often embossed with close-set hemispheres, marking the location of the contracted polyps. The tapering, tawny branches of the staghorns were crowded with starlike living forms, while the waving gorgonians, rising toward the sunlit water surface in moving forest growths of vertical branchlets, showed each slender subdivision limned as with a halo of translucent white or golden polyps (see Color Plates V and VI). These myriads of tiny creatures are the architects and builders of the coral lime- stone structure, as well as the horny sup porting substance forming the flexible gor gonian "skeleton." They, in partnership with calcareous sea plants, shell-bearing mollusks, and protozoa, are largely respon sible for the amazing submerged limestone barriers so perilous to navigators of tropic seas (see Color Plate I). The ground-up fragments of this lime stone become infiltrated between larger frag ments, and the mass is heaped up by storms to rise above the water surface, where, as dunes of wind-blown sand, they are once more hardened and cemented into laminated eolian limestone through weathering, par tial solution by acid rains, and "setting," as the result of subsequent evaporation. Seeds lodge in the crevices of the rock, soil is formed, and an oceanic island may be evolved, clothed with tropic verdure, often habitable for man. Many varying species of coral are associ ated to form the community of the living reef. What is the secret of their marvelous power to multiply their kind, the technique by which they construct their ramparts, and the mysterious source of their building materials? Over here, on this submerged ledge, where the sunlight dances through the flickering waves, a beautiful lettuce coral expands its clustered polyps like a nosegay of green and lavender blossoms. A half-dozen polyps, with partially united bodies, each an inch or more in diameter, compose the colony, and display their mottled green and brown shafts, crowned with flowerlike disks of lavender and gray flecked with white. We draw nearer and, looking through the windows of our diving helmets, examine the cluster more closely. Each individual is a cylindrical sac crowned with a circular disk, in the center of which is an oval mouth slit. A circlet of about forty-eight slender, petal like tentacles radiates from the edge of the disk and contributes to the flowerlike ap pearance of the creature. THE BIRTH OF A POLYP Some of the polyps are almost separated from their fellows, while the others are still more or less united. It is obvious that a process of division is going on, the number of individuals increasing by splitting or bud ding from each other (see Color Plate II). As we watch, a small marine worm wriggles out from a crevice and starts to crawl with rhythmic undulations over the coral.