Scientists believe that the first primitive plants appeared about 1,000 million years ago. It is difficult to be certain about the date, because simple organisms do not usually leave fossils. However, these primitive plants are thought to have laid down fossil deposits, rather like coral reefs, in shallow seas.
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Plants growing in bogs and peaty areas often need to supplement their food supply by catching insects. Bog water contains very little nitrogen, but some bog plants can obtain this substance by catching and digesting insects. They are known as insectivorous plants. Some have vase-shaped structures, into which insects are lured by bright colours and scents, like flower nectar. They fall into a slippery funnel and drop into a pool of liquid containing digestive juices. Other insectivorous plants are covered with sticky tentacles that trap flies. The most remarkable is the Venus’s flytrap plant. It has two clawed plates that slam together when a fly walks over them and touches a trigger hair.
Other insect-eating plants are aquatic, catching tiny crustaceans in bladder-shaped-underwater traps. Some of the largest insectivorous plants live in the tropical rainforests of Southeast Asia. They produce hanging, vase-shaped traps as big as a fist.
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Plants store food and water over the winter, or in dry conditions. Underground storage organs develop from roots, stems or leaf bases, and we use many of these plant organs as foods, for example potatoes and carrots. Bulbs and corms are common storage organs, which are familiar in many garden plants. Above the ground, desert plants have swollen stems or leaves in which they store water.
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Many plants are able to move their leaves slowly to keep them facing the sunlight. In same plants, this movement is very fast. The sensitive plant suddenly collapses all its leaves when touched, and looks as though it is dead. This is to help protect it from grazing animals. Other forms of movement happen when a plant distributes its seeds. Some plants can ‘fire’ their seeds for a considerable distance, making sure that the new plants do not grow too close.
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Plants living in very dry regions are specially adapted to stop them from losing too much water. They have smaller leaves, which are often thin and spiny, or they may have no leaves at all as in the case of cacti. The chlorophyll in a cactus is concentrated in the plant’s fattened stems.
Desert plants also conserve water by having a thick waxy coat over their leaves and stems, and by storing water after the rain. Some desert plants have fat, swollen leaves or stems that are filled with water. Desert plants also have extremely long roots that burrow deep into the soil.
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The process of photosynthesis takes place mostly in the leaves of a plant. Leaves are large and flattened so that a large area of chlorophyll is exposed to the sunlight Leaves are also used in a process called transpiration, which helps draw water and dissolved minerals up the plant’s stem from the roots, where these substances have been absorbed from the soil. During transpiration, water evaporates through tiny holes in the leaves. More water is drawn up through a thin tube extending down the plant’s stem.
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