The World of Plants

  Without plants there would be no other life on Earth. For only plants can make their own food using simple materials - carbon dioxide gas from the air and water and mineral salts from the ground. Animals cannot make their own food: they feed either upon plants or upon each other. Plants also provide shade and shelter: birds, insects and mammals make their homes in trees.
There are about 500,000 species of plants, and they are classified in a similar way to animals. Many species of plants share the same common names.

The Plant Kingdom

  There are several groups of simple plants: algae, which include seaweeds and the scum on ponds; fungi, such as toadstools; liverworts, and mosses. Then come the ferntype plants: ferns, clubmosses, and horsetails.
The next group of plants is called the gymnosperms, which means 'naked seeds'. They have their egg cells and pollen in cones, and include cycads, ginkgoes, and the familiar conifers. Finally come the flowering plants, known as the angiosperms, which means 'seeds in a case'.
All plants except the simplest work in the same way. A typical plant has a system of roots, which anchor it in the soil and also absorb water and minerals from the soil. The stem carries the water from the roots to the leaves. It also supports the leaves and raises them up to catch the light.
Trees, bushes and shrubs have woody stems. The wood in the middle of a tree trunk is very hard and no longer carries water, but it provides a strong support for the tree. The trunk grows a little thicker every year and you can tell the age of a tree stump by counting the number of growth rings across its trunk.