Introduction About Angiosperms

Introduction About Angiosperms Anatomy is a study of the internal structure of organs. There are between 200 000 and 300 000 different species of angiosperms (flowering plants) known. In comparison with other organisms, only insects number more species than angiosperms. Although a wide variety of flowering plants occur on earth, all have more or less the same structure and consist of three basic organs: roots, stems and leaves.Angiosperms are divided, according to certain characteristics which you studied in std.7, into two large groups, viz. Dicotyledoneae and Monocotyledoneae. In this section I shall refer to the former group as dicotyledons and the latter group as monocotyledons. In this chapter you will learn more about the anatomyRootsThe root system of a flowering plant begins its development from the hypocotyl of the embryo of the seed which gives rise to the primary root. Roots generally grow downwards into the soil (positively geotropic) and upwards (negatively geotropic).Figure 3Roots do not bear leaves and therefore no nodes are present.Two kinds of root systems can be distinguished in flowering plants: tap root systems andadventitious root systems. Usually dicotyledons posses tap root systems and monocotyledons adventitious root systems.Tap Root System: The primary root grows vertically down into the soil in the tap root system. Later lateral or secondary roots grow from this at an acute angle outwards and downwards, and from these other branches may arise. The main or primary root is known as the tap root; together with its many branch roots it forms a tap root system e.g. the bean.Adventitious Root System: The primary root usually dies at an early stage and is replaced by numerous roots that develop from the stem. These roots, which develop from the stem, are...