This name has been given to certain plants which have developed the curious habit of capturing insects and using them for food. This behavior seems at first sight most unplantlike, but it is discovered that the actual food of all plants is practically the same as that of animals. The chief peculiarity of carnivorous plants, therefore, does not lie in the food which they use, but in the methods which they have worked out for securing it.

They are all green plants, and hence are able to make food for themselves, but they live in surroundings which are poor in some of the material which they need in the manufacture of food, so that they have learned to supplement their food by capturing insects or other small animals. When it was discovered that these plants not only captured insects, but secreted substances for digesting them, it was thought to be a very astonishing fact. It is found, however, that all plants have digestive substances to act upon their food materials, and that animals are not peculiar in this regard. It would seem, therefore, that the use of such food as the bodies of insects and the digesting of this food are not facts which are peculiar to carnivorous plants, but belong to all plants as well.

It is interesting, however, to observe the various devices which plants have adapted for capturing their prey, and it is these various devices which form the subject of this paper.

Prominent among the carnivorous plants are the pitcher plants, whose leaves form tubes, or urns, or pitchers of various forms, which contain water, and to which insects are attracted and drowned. There is a very common pitcher plant in our northern bogs, in whose urn-like leaves insects are found drowned, but which does not have such elaborate arrangements for their capture as other forms. Perhaps the most famous of the pitcher plants is one which is common throughout the southern states. The leaves are shaped like slender hollow cones, and rise in a tuft from the swampy ground. The mouth of this conical urn is overarched and shaded by a hood in which are translucent spots like small windows. Around the mouth of the urn are glands which secrete a sweet liquid, and drops of this nectar form a trail down the outside of the urn. Inside, just below the rim of the urn, is a glazed zone so smooth that insects cannot walk upon it. Below the glazed zone is another zone thickly set with stiff downward-pointing hairs, and below this is the liquid in the bottom of the urn. If a fly is attracted by the nectar drops on this curious leaf, it naturally follows the trail up to the rim of the urn where the nectar is abundant. If it attempts to descend into the urn it slips on the glazed zone and falls into the water; and if it attempts to escape by crawling up the side of the urn, the thick-set, downward-pointing hairs prevent. If it seeks to fly away from the rim it flies towards the translucent spots in the hood, which look like the way of escape, as the direction of entrance is in the shadow of the hood. Pounding against the hood the fly falls into the water. This southern pitcher plant is known as a great fly catcher, and is frequently used for this purpose in the south.

The very largest of the pitcher plants is one which grows in the swamps of California, whose leaves sometimes become as much as two or three feet high, the huge pitchers forming the most capacious receptacle for insects of all kinds and sizes. Its general plan is like that of the southern pitcher plant described above, in that it has an overarching hood with translucent spots, and a trail of nectar which leads to the dangerous rim. It has become further elaborated, however, in that the hood extends into a gaudy fish-like appendage, whose colors and flapping serve to attract the flying as well as the creeping insects. The pitcher, also, instead of being straight, is spirally twisted, and has a wing-like expansion which serves as a guide in the spiral ascent to the rim, and leads the victim with definiteness and certainty to the region of danger. The fish-tail appendage is also smeared with the nectar secretion, so that any flying insect lighting upon it is enticed under the overshadowing arch and is almost sure of capture.

The most common pitcher plants of the tropics are the Nepenthes, one of which is shown in our illustration. It will be noticed that each leaf when fully formed consists of three distinct regions, namely, the leaf-like blade, which is continued into a tendril which coils around a support, and the tendril in turn ends in a curiously-formed pitcher, which has a more or less complete lid. These pitchers are often mottled with bright colors, and as they swing at the ends of the tendrils they seem to attract the attention of roving insects. Around the rim of the pitcher a very definite row of glands may be observed, which secrete the nectar to which the insects are attracted. The arrangements within the pitcher are such as have been described for the ordinary pitcher plant. These pitchers of Nepenthes are usually found containing insects, and often very many of them, whose bodies are being slowly digested and the products absorbed by the plant.

Another group of carnivorous plants consists of the sun-dews which grow in swampy regions and are quite common in our sphagnum swamps. While the pitcher plants depend upon luring insects to their death by drowning, the sun-dews depend upon stickiness. The leaves form small rosettes on the ground and are of various shapes. In one of the most common forms the leaf blade is round, and the margin is beset by prominent bristle-like hairs, each with a globular gland at its tip. Shorter gland-bearing hairs are scattered over the inner surface of the blade. All of these glands secrete a clear sticky fluid which hangs to them in drops like dewdrops, and since these dewdrops are not dispelled by the sun the plants have been called the sun-dews. If a small insect, in flying or creeping across the plant, happens to touch one of the sticky drops it becomes entangled, and then there follows a curious scene. If the insect is small, the single bristle-like hair, in whose sticky drop it has become entangled, will begin to bend inwards and will finally press the captured insect down upon the body of the leaf where the short glandular hairs receive it. If the insect is strong enough, however, to escape from a single sticky drop, neighboring hairs will bend toward the one which has captured the insect, and by adding their mite of strength and glue, succeed in detaining it until they all bend inwards and press it down upon the leaf. In some cases the whole half of a leaf will roll inwards in this attempt to secure an insect. In this position the captured insect is gradually digested and its nutritive substances absorbed.

Perhaps the most famous and remarkable of the fly-catching plants is the Venus fly-trap, known only in swamps near Wilmington, North Carolina. This fly-trap does not depend upon drowning the insects, or upon sticking them fast, but upon its quickness of movement. Of course this seems most wonderful in plants, which are not ordinarily endowed with powers of quick motion. Dionaea, for this is the name of the Venus fly-trap, has a cluster of small leaves rising from the marshy ground, just as is the case with pitcher plants and sun-dews. The lower part of the leaf is like any ordinary blade, but above becomes pinched almost in two, and then suddenly flares out again into a round blade-like expansion which is constructed like a steel trap, the two halves snapping together and the marginal bristles interlocking like the teeth of a trap. A few sensitive hair-like feelers are developed on the leaf surface, and when one of these is touched by a small flying or hovering insect, the trap snaps shut and the insect is caught.

Many interesting experiments have been performed with Dionaea to show its quickness and its recognition of suitable food material. For example, although it will snap shut at the touch of a pencil point, or any other indigestible substance, it soon opens again; while in the case of a digestible substance the trap remains closed until digestion has taken place. It has been claimed further that when the trap has closed its bristles do not interlock closely at first, so that between the crevices very small insects may crawl out and escape. In such an event the trap opens again and waits for other prey. If this be true, it follows that the leaf does not undertake the rather long process of digestion until an insect of suitable size has been captured, one which cannot escape through the meshes of the bristles. Digestion is slow work with Dionaea as with an anaconda, being said to occupy not less than two weeks.

Among the common marsh plants in certain regions are the bladderworts, so-called because their bodies are kept afloat in water by means of numerous little bladders. While these bladders are used in this fashion, they also serve as most effective traps for certain very small water animals related to the insects. Each bladder has a sort of opening which is guarded by a door like that of an ordinary rat trap. From the side of this entrance hairs are floating and waving in the water, and within the transparent bladder are other waving tufts of hairs. For some reason these things are attractive to the minute water animals, and they push aside the easily-moved trap door, and entering the bladder find escape impossible, for the door, which was easy to push aside on entering, cannot possibly be moved outwards.

It must not be supposed that carnivorous plants are peculiar in the kind of food they use, but merely in the source from which they obtain it. There are other green plants which supplement their food supply by preying upon other plants. For example, the mistletoe is able to manufacture a certain amount of food for itself, but it adds to this supply by absorbing prepared food from the trees upon which it grows. The dodder is another illustration of a high grade plant which begins life independently, but presently breaks its connection with the soil and becomes entirely dependent upon the plants around which it twines and from which it absorbs.

A great many plants are known as root-parasites, that is, they absorb from the underground parts of other plants. This is notably the case with the orchids and heaths, which have the appearance above ground of being entirely independent, but which really are quite dependent upon the underground parts of other plants.

One of the lowest groups of plants, known as the fungi, have cultivated most completely the habit of dependence on other organisms. They attack both plants and animals, and are often exceedingly destructive. Among the better known of these parasites are the rusts, which attack and destroy many of our most useful crops. To the fungi there also belong the well-known bacteria, which are the cause of numerous contagious diseases both among plants and animals. It will be observed that these parasites are using exactly the same sort of food as do the carnivorous plants. This does not appear so striking in this case, simply because the attacking plants are so much smaller than the organisms attacked that they do not seem to capture them, although they are often none the less effective in destroying them.

John Merle Coulter.