The traps of carnivorous plants are modified leaves that in some cases are so changed and adapted to their function that they resemble only remotely leaves as most people picture them. For example, the tall, often decorative tubular pitcher leaves of species of Sarracenia are frequently thought by the uninitiated to be flowers, and in most cases the trap leaves are far more striking than the plants' true flowers. This case of mistaken identity is somewhat ironic since it is accepted that most true flowers are decoratively structured in order to attract insects or other animals as pollinators. The trap leaves are also attractive to insects, but for a different end.
There are four types of traps in seed-bearing carnivorous plants of our region, and I have further divided these into two main groups, active and passive. I would reiterate that "active" is used in a restricted sense, not as it might be used in connection with animals of prey. A classification of these trap forms along with examples is in outline form below and can be correlated with the accompanying photographs and drawings. Active traps. —Those in which some rapid plant movement takes place as an integral part of the trapping process.
1. Closing traps. —These are often referred to erroneously as of the beartrap type. The trap is bivalved; that is, it has two similar halves connected by a midrib. The two halves close on each other and thus trap the prey. This type is represented in the western hemisphere by only one species, Dionaea muscipula (the Venus' flytrap).
2. Trapdoors. — These are aquatic traps, relatively minute, and are represented by the genus Utricularia (the bladderworts). The trap is somewhat bulbous, with a flaplike door over a small entrance at one end. The stimulation of sensitive external trigger hairs near the trap entrance results in the opening of the door and an inrush of water with the prey. Afterwards, the door closes again.
Passive traps. —Those in which rapid plant movement is not an integral part of the trapping process.
3. Pitfalls. — These are characteristic of the familiar pitcher plants of the genera Sarracenia and Darling-tonia. The leaves are tubular with various other modi-
Fig. 1-1. Dionaea muscipula, the Venus' flytrap, with a trap of the closing type.
Fig. 1-2. Utricularia gibba, a bladderwort, with a trap of the trapdoor type. The plant is aquatic and the bulblike trap is only 2-3 mm.
fications. The prey is lured to the pitcher opening, enters or falls in, is unable to escape, and is digested. 4. "Flypaper" or adhesive traps. —These occur in Drosera (sundews), and Pinguicula (butterworts). Numerous sticky glands cover the upper leaf surfaces, and the small prey is immobilized by becoming mired down. After entrapment, the stalked glands of Drosera do often move slowly and there frequently is some slow leaf folding in some species, but this is part of the digestive rather than the entrapment process.
This brief outline is for orientation; details of various traps and their activities will be discussed in the ensuing chapters.
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