Delphinidin

Highly specialized insect-trapping leaves have intrigued humans for hundreds of years. Almost 200 species of flowering plants are known to have these leaves. Insectivorous plants grow mostly in swampy areas and bogs of tropical and temperate regions. In such environments, certain needed elements, particularly nitrogen, may be deficient in the soil, or they may be in a form not readily available to the plants.

Some of these elements are furnished when the soft parts of insects and other small organisms trapped by the specialized  leaves are broken down and digested. All the plants have chlorophyll and are able to make their own food. It has been demonstrated that they can develop normally without insects if they are given the nutrients they need. The following plants represent four types of insect-trapping mechanisms.

- Pitcher Plants
The blades of leaves of many pitcher plants are flattened and function like those of any other leaves. Some of the leaves of these curious plants, however, are larger and cone-shaped or vaselike. In some species, these larger pitcher leaves have umbrella-like flaps above the open ends, but the flaps don’t prevent a little rain water from accumulating at the bottom. Some Asian pitcher plants are vines with leaves whose long petioles are twisted around branches for support.

Their pitchers are formed at the tips of the leaves. Pitcher leaves have nectar-secreting glands around the rim. The distinctive odor produced by these glands attracts insects, which, while foraging, often fall into the watery fluid at the bottom. If the insects try to climb out, they find the walls highly polished and slippery. In fact, the walls of some pitcher plant leaves are coated with wax, and as the insects struggle up the surface, their feet become coated with the wax, which builds up until the victims seem to have acquired heavy, clodlike boots. Most insects never make it up the walls, but even if they do, they still face a formidable barricade of stiff downward-pointing hairs near the rim.

Eventually they drown, and their soft parts are digested by bacteria and by enzymes secreted by the plant's digestive glands near the bottoms of the leaves. In North America, the pitcher plants produce their pitchers in erect clusters on the ground, but the mechanisms for trapping insects are similar to those of Asian species. Malaysian tree frogs, which have sticky pads on their feet, are undaunted by pitcher-plant leaves and lay their eggs in them. The eggs contain a chemical that neutralizes the pitcher’s digestive enzymes.

Merchandisers have been shameless in their wholesale collection of these plants for sale, and pitcher plants may become extinct in the wild. The cobra plant, a pitcher plant restricted to a few swampy areas in California and Oregon, as well as two other species, have been placed on threatened species lists.

- Sundews
The tiny plants called sundews often do not measure more than 2.5 to 5.0 centimeters (1 to 2 inches) in diameter. The roundish to oval leaves are covered with up to 200 upright glandular hairs that look like miniature clubs. There is a clear, glistening drop of sticky fluid containing digestive enzymes at the tip of each hair. As the droplets sparkle in the sun, they may attract insects, which find themselves stuck if they alight. The hairs are exceptionally sensitive to contact, responding to weights of less than one-thousandth of a milligram, and bend inward, surrounding any trapped insect within a few minutes. The digestive enzymes break down the soft parts of the insects, and after digestion has been completed (within a few days), the glandular hairs return to their original positions. If bits of nonliving debris happen to catch in the sticky fluid, the hairs barely respond, showing they can distinguish between protein and something "inedible."

Some sundew owners regularly feed their plants tiny bits of hamburger and boiled egg white. In Portugal, relatives of sundews with less specialized leaves are used in houses as flypaper. In response to contact by living insects, the edges of specialized leaves of similar plants called butterworts rapidly curl over and trap unwary victims.

- Venus’s Flytraps
The Venus’s flytrap, which has leaves constructed along the lines of an old-fashioned steel trap, is found in nature only in wet areas of North Carolina and South Carolina. The two halves of the blade have the appearance of being hinged along the midrib, with stiff, hairlike projections located along their margins. There are three tiny trigger hairs on the inner surface of each half. If two trigger hairs are touched simultaneously or if any one of them is touched twice within a few seconds, the blade halves suddenly snap together, trapping the insect or other small animal. As the creature struggles, the trap closes even more tightly. Digestive enzymes secreted by the leaf break down the soft parts of the insect, which are then absorbed.

After digestion has been completed, the trap reopens, ready to repeat the process. Venus’s flytrap leaves, like those of sundews, do not normally close for bits of debris that might accidentally fall on the leaf, because nonliving material does not move about and stimulate the trigger hairs.

- Bladderworts
Bladderworts, which are found submerged and floating in the shallow water along the margins of lakes and streams, have finely dissected leaves with tiny bladders. The stomach-shaped bladders are between 0.3 and 0.6 centimeter (0.125 to 0.25 inch) in diameter and have a trapdoor over the opening at one end. The trapping of aquatic insects and other small animals takes place through a complex mechanism.

Four curled but stiff hairs at one end of the trapdoor act as triggers when an insect touches one of them. The trapdoor springs open, and water rushes into the bladder. The stream of water propels the victim into the trap, and the door snaps shut behind it. The action takes place in less than onehundredth of a second and makes a distinct popping sound, which can be heard with the aid of a sensitive underwater microphone. The trapped insect eventually dies, is broken down by bacteria, and the breakdown products are absorbed by cells in the walls of the bladder.

Science-fiction writers have contributed to superstitions and beliefs that deep in the tropical jungles there are plants capable of trapping humans and other large animals. No such plants have been proved to exist, however. The largest pitcher plants known hold possibly 1 liter (roughly 1 quart) of fluid in their pitchers, and small frogs have been known to decompose in them, but the trapping of anything larger than a mouse or possibly a small rabbit seems very unlikely.

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