The Open Door Web Site
Part IV : How Plants Feed
Sundew, Jardin des Plants, Paris
Pitcher Plants, Jardin des Plants, Paris
Venus' Flytrap, Jardin des Plants, Paris
PLANTS WHICH FEED IN DIFFERENT WAYS
Most flowering plants are green but a few manage to survive without chlorophyll.
A few plants manage to survive without chlorophyll. Some of them, such as the broomrape and the dodder, are parasites. They have special roots which penetrate the body of another living, green plant to suck its sap. This is how parasitic plants feed. They do not photosynthesize themselves so they do not make any chlorophyll.
Lichen, Antarctic Peninsula
Lichens are formed by a partnership between two organisms, certain fungi and certain simple, green plants called algae (singular: alga). The fungus provides the support for this partnership and the alga, through photosynthesis, feeds both of them.
These two organisms, the fungus and the alga, live so well together that they grow better combined as a lichen than they would do on their own. When this happens we call the relationship mutualism or symbiosis.
It is true that some plants capture and eat insects and yet they are also coloured green with chlorophyll. This is because these plants grow in soil which is very poor in mineral content, especially nitrogen and phosphorus. Many carnivorous plants are found living in bogs where the soil is lacking in many essential minerals. These plants obtain their supply of nitrogen and phosphorus from the bodies of the insects they trap with their specialized leaves.
Therefore, carnivorous plants make organic matter for their bodies by photosynthesis and they eat insects to obtain certain minerals.
The Sundew is a carnivorous plant which is found in Europe. It has leaves which are brightly coloured to attract the insects. These leaves are also covered with sticky hairs which trap the insects which land on them.
The pitcher plant is a carnivorous plant which drowns its victims. Its leaves are shaped like tubes and they collect rain water. There is a sweet substance around the rim of each tube which attracts insects. Once the insect enters the tube it is prevented from escaping by small, slippery hairs which point downwards.
Pitcher plant, Bristol Zoo, UK
Eventually the insect exhausts itself by its effort to escape and slides into the water. The pitcher plant releases juices into the water to digest the insect.
The Venus' flytrap from the United States is perhaps the best known carnivorous plant. It has a few specialized leaves which are divided into two distinct halves. Each half leaf has three 'trigger' hairs on it. If an insect which lands on the leaf touches two of these hairs, the two halves quickly fold trapping the insect between them. The rim of each half leaf has thick hairs which curve slightly upwards when the leaf is open. When closed these hairs form a barrier, like the bars of a prison, to prevent the insect escaping.
The leaf produces juices which break down the soft parts of the insects body and the minerals are absorbed. Eventually the leaf re-opens and the dry, undigested parts of the insect are left to blow away in the breeze.
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