Interesting Plants

Trigger Plants

This is an interesting group of plants (Stylidium), whose flowers are touch-sensitive to the probing of insects. The male organ containing pollen is placed under tension and positioned below the petals. As a butterfly or other insect probes the floral tube for nectar it triggers a lightning response, whereby this male part flings up and slaps the insect on the back, thus depositing the pollen onto the insects body. The insect then flies off to another plant and transfers the pollen to another flower, enabling pollination to occur.

Carnivorous Plants

Carnivorous or insect eating plants catch and digest small insects. These plants grow in places where there is little nitrogen available in the soil, so they supplement it by digesting the protein of the animals they catch.

Pitcher Plants

There are a number of species of pitcher plants and the pitcher may vary from being as small as a thimble to as large as a jug. The edge of the pitcher is rounded and on its inner side the cells are covered with minute scales of wax. When an insect walks on the edge of the pitcher its feet become covered with these scales and it is completely unable to gain a foothold. As a consequence it slides down the pitcher into the digestive fluid below.

Despite these trapping and digestive activities there are some animals that can live within the pitchers. At least four kinds of spiders are known that can spread their webs across the opening and catch the insects entering the pitchers. There are also a number of small animals that have been found living in the pitchers, three of which have never been found anywhere else. They feed on the insect remains in the pitchers and are somehow able to protect themselves against the digestive juices.

Australia has two pitcher plants, a ground plant in Western Australia (Cephalotus follicularis) and a climber in Queensland (Nepenthes mirabilis).

Sundews

Sundews (Drosera) are found in many parts of the world, particularly in Australia. The sundews form rosettes which bear central flowering stems with small white flowers. The upper surface of the leaves is covered with ‘tentacles’ and the heads of these are covered with a drop of sticky secretion. Insects alight on the leaves, touch the drops and are unable to get away. These drops glisten in the sun and are thus responsible for the name sundew.

When an insect is caught, other nearby tentacles are stimulated to bend towards it and the leaf margin curls so that the insect is effectively trapped. The tentacles also produce a digestive fluid and when the digestion of the insect is finished the tentacles unfold and the trap is once more set. Venus Fly Trap

The Venus Fly Trap (Dionaea muscipula) is probably the most fascinating of all carnivorous plants. The plant grows in bogs in the south-eastern United States. The leaves are spherical in shape and consist of two parts. When an insect touches the leaves they instantly close like a spring trap and this confines the insect. On the upper surface of each leaf are three sensitive bristles. Two of these must be touched within about twenty seconds to cause the half leaves to close. Closure takes place within less than a second. Numerous glands on the leaves give out digestive juices, which act on the trapped insect, and the products of digestion are rapidly absorbed.

Acknowledgements

Burton, M. (1966) Nature, The Grolier Society Ltd., London, UK.

Darnowski, D. (2002) Trigger Plants, Rosenberg Publishing, NSW, Australia