Part 24

The rarest plant in North America, found only four times by botanists, is a ground-hugging desert flower—the gold carpet. The plant appears, on rare occasions, in California’s Death Valley. Its appearance is that of a rosette of yellow leaves, sometimes as much as ten inches in diameter, lying flat on the ground. From this rosette arise innumerable tiny golden yellow blossoms, so that the whole seems like a patch of golden carpet in the brown desert. The reason for its rare occurrence is that its seeds can germinate only after a good rain. Such rains are rare in its habitat.

The plants must spring up within a few days. Ordinarily, even then, they die with the increasing drought before blossoming—thus forming no seeds. In order for them to produce the seeds for another generation there must be another rain following shortly upon the first.

The seeds become buried in the desert soil and, in the course of evolution, have developed the capacity of suspended animation over a number of years. In the old days, it is probable, these seeds retained their fertility only for a single season. Now there may be several years between rains sufficient to spur them to germination, and even longer periods between double rains which will enable them to form seeds.

The strange little plant first was discovered in 1891. There were only two specimens and search failed to reveal any more. Two years later, however, at about the same place another single plant was reported. No others were revealed by an intensive search through the entire area.

In 1931 and 1932 Dr. Frederick V. Coville of the U. S. Department of Agriculture and French Gilman, a California botanist, again made an intensive search but could not find a single plant. They came to the erroneous conclusion that the plant might be native to the mountains, from which occasional seeds were washed down after heavy rains. A few years later Mr. Gilman again took up the search and succeeded in locating the plant in four places. He found 14 individuals altogether and watched their growth carefully. Only three became large enough to flower and produce seed. The others dried up and died when they had only a few leaves and no branches. Later, however, Gilman found many specimens of the gold carpet scattered over low hills in the neighborhood.

These little hills all were whitish in color. This led to the idea that the chemical composition of the soil might have something to do with the appearance of the plants. Analysis, however, showed there was no basis for this assumption.

In the distant past, the gold carpet may have been a very abundant plant, germinating and flowering annually in a reasonably moist climate. Probably a few individuals developed the capacity of producing seed which would remain fertile over a lapse of years. When the climate changed these had a decided advantage over their fellows.

Apparently the gold carpet is a plant in the process of extinction. The continued existence of the species depends on the dormancy of a sufficient number of seeds to carry it over unfavorable years of inadequate, or inappropriately timed second rains. If Death Valley becomes drier and drier and years with suitable double rains become more and more infrequent the vitality of the seeds in the soil eventually will be insufficient to span the long periods when no seeds are produced.

Evolution of the Bird

It’s a long call from the birds with teeth that hovered over the strange world of the dying dinosaurs 150,000,000 odd years ago to the chorus of sweet singers whose music opens sleepy eyes on May mornings of the present. The long and devious road can be traced from the grotesque archaeopteryx and archaeornis—nightmare-like and long extinct flying creatures of the dawn—to the living wren and blackbird. But however complicated, the family tree of birds is simple compared to that of the reptiles or the mammals, since avian evolution has been confined within narrower lines.

Up to the time that the monster reptiles were beginning to disappear, it seems probable that all birds had teeth. Gradually, they disappeared as the group advanced into the dawn age of present life forms. First were the ancestral birds—the archaeornithes. They were essentially winged reptiles. Following them came the toothed true birds of the New World, known from very fragmentary fossil records. They included the hesperornis, the hageria and the ichthyornis. Then, representing a long advance, came creatures of the ostrich family, probably the most primitive of living birds. They are true birds but have not reached the typical modern pattern. At the top of the family tree, the highest branch of bird evolution, is the great sub-order of song birds. It includes fifty families ranging from the larks to the finches and buntings.

Speed Ace of the Air

The swiftest bird flight ever recorded accurately is in the neighborhood of 175 miles an hour. Ordinary, unhurried flight averages from twenty to forty miles an hour.

The fastest flyer, according to official records, is the California duck hawk whose speed was measured with a stop watch from an airplane. Eagles apparently are much slower.

Among the more reliable bird flight speed measurements are those of herons, hawks, horned larks, ravens and shrikes. Rates range from 22 to 28 miles an hour. Flight in all these cases was normal and unhurried. Other speeds reported by the Smithsonian are: crows, 31 to 45 miles an hour; starlings, 38 to 49 miles; geese, 42 to 55 miles; ducks, 44 to 59 miles; falcons, 40 to 48 miles.

When frightened, most birds probably can nearly double their normal rate, but they cannot keep it up very long. When cruising about in search for food they fly so as not to waste their strength. This is particularly true on the great annual migrations.

Considering ten hours as a fair day’s flying time over land, the measured speeds would carry crows from 310 to 450 miles between sunrise and sunset and ducks and geese from 420 to 590 miles. Considering that they fly in straight lines, this means that they make very good time from point to point. It is highly probable, however, that most migrating birds proceed in a leisurely manner and that after a flight of a few hours they pause to feed and rest.

The Remarkable Instincts of the Silk Worm

The silk worm’s brain has an instinct center contained in a speck of nerve cells with a mass of less than a millionth of an ounce. This center is a microscopic so-called “mushroom body”, found in both sides, or hemispheres, of the brain. The discovery, with possible far-reaching philosophical implications, came out of some of the most delicate conceivable microsurgery in which the area was destroyed almost cell by cell by means of an invisibly fine electric needle.

Doctors Carol Williams and William Van der Kloot of Harvard have made minute studies of an American silk worm, the cecropia (common along the Atlantic coast), which spins as strong and delicate threads as the Japanese or Italian domesticated silk worms. The cocoon is a marvel of apparent ingenuity, made of a single thread almost a mile long. It is made in three layers, roughly after the design of a thermos bottle. The outer layer is a tightly woven, waterproof silk bag. Inside this is a layer of loosely spun material which serves as an insulating layer. The third layer, woven around the body of the worm itself, is a bag of exceedingly fine, soft silk. Through each layer a “hatchway” is provided directly in front of the creature’s head. These must be placed one in front of the other with mathematical exactitude. Through them the self imprisoned animal must escape when the time comes, and the slightest error probably would make it a prisoner forever in a coffin of its own creation.

Inside the cocoon the worm remains, adequately protected from cold and damp, for nine months. It emerges as a winged moth, whose sole function in life apparently is to lay eggs to produce more silkworms.

Spinning such a cocoon with its three quite different layers requires extreme precision of movement. Nature has not allowed for any possible variations. Yet the masterpiece obviously is not the result of any thinking, education or practice. The little worm’s life span, for one thing, would not allow for any training. Every movement must be instinctive and presumably unconscious, directed by the same part of the nervous system into whose structure the pattern has been built by nature.

The house building must start at precisely the right time. Until that time, according to the Harvard physiologists, the responsible area of the brain is held in restraint by a hormone secreted from two tiny glands in the head. At the foreordained instant this inhibiting secretion ceases and the mushroom body can go into action. The spinning can be started at any time, however, by destroying the glands.

Williams and Van der Kloot tried effects of two gasses, carbon dioxide and carbon monoxide. Both acted as potent brain depressants, but in quite different ways. The first eliminated the spinning behavior entirely and permanently. The worms wandered about aimlessly, apparently trying in vain to remember what some overwhelming internal drive was pushing them to do. The automobile exhaust gas, carbon monoxide, fatal to humans but without any serious lasting effects on invertebrates because of the lack of the red cells in the blood with which it combines in higher animals, caused them to spin a worthless and meaningless flat layer of silk as long as the effect continued. When this ended the worm started to spin what remained of the mile-long thread in the customary pattern, starting from the point it normally would have reached had it not been gassed.

The biologists then resorted to their unbelievably delicate surgery. They proceeded to destroy the silk worm brain a few score cells at a time. The brain contains hundreds of thousands of cells. The destruction had no effect on the spinning behavior until they reached the mushroom body. When a few cells of this area were killed by the electric current the worm no longer could spin a cocoon but continued to wind and weave its silken thread into three flat sheets, corresponding to the three normal capsules. The weaving continued with the destruction of a few more cells, but only in a single sheet. When a few more were destroyed the entire cocoon-making behavior came to an end.

Thus, Doctors Williams and Van der Kloot concluded, they had located a physical unit of behavior. Within it was capsuled the whole “memory” of the silk worm race with respect to spinning. More than a century ago this mushroom body was discovered by the French physiologist Dujardin, who called it the “seat of instinct.” At that time this was only a wild speculation on his part, without any supporting facts whatsoever.

The instinct center is found in the brains of all insects in whom group instinctive behavior has manifestation. In the honeybee worker, intellectual giant of the insect world, it reaches its greatest size. In drones and queens, who do not display much behavior of any sort, the area of the brain is quite small.

The Strange World of the Sea