PLANTS EAT FLESH

Evening Star, Issue 21544, 17 October 1933, Page 1

PLANTS EAT FLESH

GROWTHS OF TROPIC JUNGLES When an animal bites a plant, that is hardly news. But when a plant bites an animal there may be an interesting story in it. There are, indeed, a great many interesting stories that might be told of plants that eat animals, in spite of the fact that there are not many such plants, and that the most widespread and sensational of such stories are not true (writes Dr Frank Thone, in the ' San Francisco. Chronicle '). The tales about the man-eating tree of Madagascar are about the most completely hardy perennial species in all popular pseudo-scientific literature, and also about the most completely unproved. They go with the similar yarns about the deadly Upas tree of the East Indies—the tree that was said to knock down men and animals with its mere poisonous breath. Both the Madagascar monster, and the jioisoh-scented Upas tree must go i the way of all myth. There are no I trees that destroy men, but there are, | all over the world, many smaller plants i that regularly make meals of insects and other small animals' forms. Some of these carnivorous vegetables live in the tropics, or in those strange remote lands " down under," Australia and South Africa. But there are many of them in America. Some of them live in the water, and the rest, without exception, live in bogs. That is the secret of the strange bloodthirsty habits of these plants—bog water. Bog water- is acid, and for some reason not j-et well understood acid water prevents roots from getting nitrogen, which all plants must have. One of the principal constituents of animal ilesh is this same nitrogen. It is primarily to get,it that we ourselves eat meat and eggs and cheese, and it is to' get nitrogen that some of the nitro-gen-starved plants of bogs and acid ponds have developed their uncanny ability to capture and digest insects and other creeping and swimming things,. Botanists have known about the flesheating habits of some plants only within comparative]}' recent times. Some of the plants they knew, but they did not realise what their strange behaviour really meant. Erasmus Darwin, for example, the clergyman-naturalist, who was grandfather of the great prophet of evolution, wrote in 1790 that the sticky tentacles of, the sundew _ were of use to the plant by preventing insects from eating the leaves, and that the hollow leaves of the pitcher plants were simply water containers. He apparently had no suspicion of their true nature. However, his famous grandson amply Redeemed the family reputation this respect, for one of his best books is on 'lnsectivorous Plants.' .In this work everything known at the -time •about--plants that eat animals was summed up in a most masterly fashion. Since Darwin's day, of course, many other students have given these plants their attention. The latest effort has been on the part of Professor E. E. Lloyd, of M'Cill University in Montreal, who recently summed up all the modern advances in our knowledge of carnivorous plants before the Royal Society of Canada, and illustrated his remarks with motion pictures of his own taking. • These pictures, are among the most remarkable of. Nature films ever made. We have grown used to jungle pictures of figlits between 1 tigers and wafer buffalo, cobras'and. mongooses, and so on. But never before have men been privileged to see movies of the deadly work that goes on'in the little jungles underfoot, where plants kill animals and devour their flesh. ' ■ ■ ' In his survey of the world for plants that eat animals, Professor Lloyd found some 440 species, belonging to sixteen genera and grouped into five plant families. This is really an exceedingly small array, considering , the hundreds of thousands of plant species known, and the probably large number of species still undiscovered. It may perhaps be taken as an indication of how hard it was for plants to learn the trick of getting their food by killing. VARIOUS METHODS. Professor Lloyd classifies all carnivorous plants into two main groups—passive traps and active traps. . The passive traps catch their prey either by secreting sticky substances that act like fly paper or by arranging pits into which the insects tumble and cannot get out again. There are three types of active traps—plants that add aggressive movement to the fly paper arrangement of the 'first type of passive traps, plants that snap shut on their prey like steel traps, and plants that cage their prev. Of the first of these five kinds of insect traps there are no. examples easily reached in America; and they are, "in any case, the least interesting of the insect traps. The second type, however —the pitfall trap—is exceedingly common in some parts of the United States and Canada; and it is, moreover, the largest and most conspicuous of all the carnivorous plants. Plants belonging to this class are mostly to be found in the various ' genera of pitcher-plants. Pitcher-plants grow abundantly in bogs wherever they occur in Canada, southward through the Great Lakes region and on down into _ Kentucky and Florida. 1 The most striking thing-about them, even to the casual observer, is the structure of their leaves. These are hollowed into graceful vase-shaped " pitchers," with a projecting flap down one side to take the place of the handle. On the upstanding " lip" of the pitcher, and again around a zone within there are multitudes of down-point-ing bristles, against which' no insect could possibly climb. Below that is an | area without bristles, but too smooth for frantic insect feet to clutch. Below this again is another bristle-set zone. To make the trap more attractive

near the rim are many glands that secret nectar, like that of a flower, a stuff of which insects are notoriously fond. More sinister is the purpose of other glands, found abundantly farther dawn the pitcher. They secrete a ferment of eutymo which digests flesh just as the pcpljn of our own stomachs does. Even more widespread than the pitcher plants are the sundews. These plants grow on wet soil almost all over the world, wherever the chemical reaction is acid enough. Most of them are quite tiny plants—> seldom more than a couple of inches across the whole rosette of their tiny leaves, or more than that high to the top of their little spire of flowers. Their leaves are either round or paddle shaped, and each leaf has a fringe of projecting little fingers around its edge, and similar fingers all over its surface. Each of these tiny fingeis ends in ;a gland that secretes a sticky stuff that holds any gna't or other tiny insect that touches it as tanglefoot .flypaper holds a fly. Bur the action of the sundew trap is not the merely passive action of flypaper. When one or more of its sticky-tipped lingers catches an insect, the insect naturally struggles. Then other fingers in the neighbourhood, stimulated by the movement, slowly bend in its direction, and each sets its sticky top on the luckless victim, pinning him yet more, firmly. Perhaps most famous of all the carnivorous plants is the Venus flytrap, which is found only in a limited area of the coastal plain of the Garolinas, principally around the eitv of Wilmington, N.C. The leaves of this plant 'are perfect counterparts of the steel traps used by fur-trappers of the north. Each is divided at its outer end into a pair of semi-circular, hristle-edged flaps that hinge along the midrib atid can close together in as little time as, half a second. Each of these flaps'has three bristles on its surface, which are the triggers of the trap. When an insect alights on a leaf, op a caterpillar crawls up along the stem, it cannot avoid touching these trigger bristles. When it touches the first one, nothing happens. But a second or so later it touches another. The two stimuli, following one on the other within a stated time, trip the internal mechanism, whatever it may be, and the two halves fly together. The bristles on the outer edges interlock like the teeth of an alligator, so that there is no chance for even a small insect to crawl out. And then the two halves of the leaf at .first concave with a little space between them, press together tightly and the digestive glands pour out their corroding juices.