WHAT IS CARNIVORY?
What is plant carnivory? Or specifically, what characteristics must a plant have to be called carnivorous? Carnivorous means literally "meat eating." When this definition is applied to plants it evokes visions of snarling green jaws snapping at nearby animal life. Although the vision is vivid, it is not in keeping with reality. Most plants are subtle in their means of entrapping animal prey and have evolved sophisticated means of digesting it; Dionaea is the proverbial exception.
A good working definition of a carnivorous plant is needed'and must account for the following characteristics: attracting prey (lures, odors, and directional guides), trapping of prey, secreting digestive enzymes and absorption of digested materials. A realistic definition of plant carnivory should be based on whether animal nutrients are digested by enzymes produced by the plant. The means of digestion varies in this group of plants. While in some digestion is the result of secreted enzymes and bacterial action, in a few it is totally attributable to bacterial action. At the present time the number of known digestive enzymes secreted by carnivorous plants varies from five in Nepenthes to none in Heliamphora. In all plants categorized as carnivorous the digestive organs are modified leaves.
One plant which is not carnivorous has seeds that are carnivorous. John T. Barber and colleagues discovered that dead mosquito larvae were attached to single seeds of Capsella bursa-pastoris. The larvae were attracted to the seeds by a chemical released by the seed and killed by a toxin produced by the seed. In addition, the seeds secrete an enzyme which digests protein of the larvae and which permits them to subsequently absorb the material. In the plants' natural environment mosquito larvae are not common, so research was continued with organisms such as protozoans, nematodes and motile bacteria which the seeds are more likely to encounter. Preliminary results show that these seeds are able to attract, kill and digest some of these organisms.
There are plants that appear structurally similar to those classified as carnivorous. Although some species of these genera might be carnivorous, this aspect of their nature has not yet been investigated. Some genera containing species in this category are listed below, classified by their type of trapping mechanism. PLANTS DISPLAYING PASSIVE TRAPPING CHARACTERISTICS
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