The Pitcher Leaf

The blossoms are usually the brightest and most conspicuous part of flowering plants. But in the Sarracenia it is the leaves, with their graceful shapes and vivid colors, that are most striking. Like flowers, pitcher leaves have glands that give out a sugary nectar that attracts insects. These glands, and a variety of other devices on the outer and inner surfaces of the leaf, lure and trap their prey.

There are some variations in the different Sarracenia species, but the yellow trumpet plant shows the basic pattern that they share.

The leaves of Sarracenia plants grow in clumps, called rosettes, from a rhizome, or underground stem. The rhizomes continue to live and grow for many years, sending up new leaves and flowers each spring at the onset of the growing season. The leaves of the yellow trumpet are long tubes, standing upright and becoming wider toward the top. A hood, attached to the back of the pitcher mouth, bends forward slightly to hang over the opening.

Pitcher Plant DiagramPitcher Plants Upright Nepenthes

The outside surface of the pitcher plant leaf has microscopic glands that produce nectar. Toward the top of the leaf the glands become more numerous and the flow of nectar is heavier. A flying insect that chances to land on any part of the leaf or a ground-living insect that wanders up to investigate is gradually led by the path of nectar toward the mouth of the trumpet. Heavy veins, more or less red in some species, and the narrow wing that runs up the front of the leaf serve as pathways for visiting insects. Both are thickly baited with nectar glands.

The inner surface of the leaf continues the design that lures these small animals toward the trap. The hood that forms a roof over the tube below contains more nectar glands and draws insects farther into the leaf. This portion of the leaf is fuzzy to the touch, covered with small hairs that offer a sure foothold and encourage further exploration. All of the hairs point downward into the tube.

The area ringing the mouth of the pitcher provides the main attraction for an insect searching for nectar. A curled-under rim, called the nectar roll, surrounds the open mouth. At the rear of the mouth a

The yellow trumpet, Sarracenia flava, grows in a wide band along the coastal plain of the southeastern states, from the corner of Virginia to southern Alabama. Leaves are often 2 to 3 feet tall. Usually they are pale green or yellow with red markings near the top of the pitcher, but some populations of this species show a variety of other coloration.

Leaf Pitchers Diagram

column of leaf tissue supports the hood. This part of the trumpet, a narrow zone less than one inch wide, is also crowded with nectar glands. They are so dense that this area is sometimes wet with nectar. Here there are no hairs; the surface is smooth, waxy to the touch—and slippery.

Any insect that loses its foothold while feeding at the mouth of the pitcher plant is in danger. Below the mouth is a chute, its walls covered with a shiny wax. It continues for several inches, becoming increasingly narrow. The space is so tight that an insect can barely stretch its wings to attempt flight. Glands line the walls of this slide area too, but these produce a digestive juice, or enzyme, that runs down and collects in the bottom of the tube.

When the struggling insect falls to the very bottom section of the leaf, it has little or no chance to escape. The walls here are hairy; but all the hairs are long and pointing downward, resisting any effort by the insect to walk against them up the tube.

During the growing season, this bottom part holds the fluids containing the digestive enzymes. The enzymes help to break down the protein in the insects' bodies. Most of the Sarracenia species produce effective digestive juices; in the species that do not, the bacteria brought in on the bodies of the victims cause a more gradual decay. The fluids produced by several of the species also contain a substance that stuns and quiets the fallen prey. As insects begin to fill the well, the plant responds by producing more liquid. The animal materials are gradually dissolved until only the very hardest parts, such as the legs of beetles, remain in the pitcher.

These digestive juices continue to dissolve the insect bodies even if rainwater pours into the pitcher and weakens their strength. In some species of the Sarracenia the enzymes are very powerful: One scientist reports opening a pitcher leaf and finding a snail shell that had been partly dissolved!

As the pile of partly digested insects in the pitcher grows, so does the odor. This too works to the plant's advantage, for now other sorts of insects, those that feed on dead animals, are tempted to enter the leaf. Some of these carrion feeders will also lose their foothold on the waxy slide and plunge down into the pitcher trap.

Most of the leaf's inner surface is covered with cuticle, a waxy material that makes the walls waterproof. However, no cuticle covers the walls in the bottom of the pitcher. There the leaf walls can absorb the pitcher liquid along with the minerals from the dissolved insects that it contains.

Laboratory work has shown that nitrogen taken in through the walls of the pitcher leaf is used through-

The purple pitcher plant, Sarracenia purpurea, is the only Sarracenia that grows naturally in the northern states. The curved leaves are from 2 to 18 inches long.

out the plant's system to meet its nutritional needs. Perhaps these plants also use other minerals from the bodies of their victims. Most of the pitcher species have not been studied thoroughly, and this is one of the unanswered questions about the way they function.

A few other groups of plants trap insects and use their bodies for food. Some of these, the small blad-derworts and sundews in particular, are widespread in this country. The famous Venus flytrap lives in a very small and shrinking part of the coastal plain of North and South Carolina. All of these other carnivorous plants are much smaller than the pitchers, but a hands-and-knees search usually discovers one or more of them in areas where pitcher plants grow. They all live in these places for the same reason: They have a resource not available to most other plants that gives them an advantage in a mineral-poor habitat.

flower of the horned bladderwort

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