Tuesday, April 1, 2008

Carnivorous Plants

Carnivorous plants are various types of flowering plants and fungi that capture and digest prey animals. Photosynthetic carnivorous plants live in habitats poor in minerals, and they benefit primarily from mineral nutrients gained from the prey. Since the animals they capture are chiefly insects, carnivorous plants are sometimes called insctivorous plants. Some species, however, capture mollusks such as slugs, or even vertebrates such as small frogs and birds.

How to capture?

Trap types observed in carnivorous plants include pitfails and "lobster traps," adhesive traps, and various kinds of mechanical traps.

Pitfalls consist of tubular leaves, or arrays of leaves, that filled with water. Insect are capture when they fall into the fluid, which often contain wetting agents and digestive enzymes. So-called lobster pots also consist of tubular leaves. In this type of trap, however, the tube is often horizontal and is lined with hairs that guide the prey along a path leading to the digestive part of the trap. Some bromeliads have leaf bases that form definite cups in which water accumulates. Such plants do not trap insects, however, so much as simply make use of nutrients provided by dead vegetation and animal remain that fall into the cups.

Adhesive traps involve sticky surfaces. Sticky haired adhesive traps exist in several plant families. Typically flying insect are capture when they adhere to slime secreted by hairs covering the leaf. In some genera, such as Drosera, the leaf actively moves the prey to the center and wraps around it. Sticky seeded adhesive traps have only recently been observed but may be widespread. The seed of the shepherd's purse. Capsera, a common lawn weed, attracts, captures, and utilizes nutrients from prey, soil bacteria do the digesting.

Mechanical traps include so-called snap traps, such as those of Venus's flytrap. In these plants the prey is trapped by rapid closure of a set of lobes aroung the animal when it touches sensory hairs that trigger the closure. The action results from acid growth in the lobes within less than a second. Suction traps, found in aquatic Bladderwort Ultricularia, are similar to the style of mouse trap. The prey trips a lever on the plant "door," which allows water and the prey to be sucked into the trap when the plant's concave side puffs outward. Snare traps are found in carnivorous fungi. One type, in the genus Arthrobotrys, has a trap that looks like a small lasso with three segments around the loop. When triggered by a nematode, the segments bulge out to capture the worm. The fungus then grows into the prey and digest it.

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