FLOWERING PLANTS

 

     The flowering plant show great variety and diversity of forms. However, they carry on the same basic activities and in spite of their seeming diversity, they exhibit a great similarity in their structure. All the activities of the different part of the plants are so co-ordinated that the plant can live, grow and reproduce as a unit. 

     A typical flowering plant consist of the vegetative and the reproductive organs. The vegetative organs are the roots, stem and leaves. While the reproductive organs are the flowers, which are concerned with the production of fruits and seeds. 

A TYPICAL FLOWERING PLANT: 

THE BALSAM

     The balsam (Impetiens balsamina) , a simple herbaceous flowering plant, consists of an axis which at one end becomes an underground root system and at the outer end, an aerial shoot system. This is the basic plan of the structure of all flowering plants. 

         THE ROOT SYSTEM

     The root system is made up of the stem, the leaves, the flowers and the fruits. The stem of the balsam is fleshly and light green in colour. It is made up of nodes and internodes. Leaves arise from the nodes and are arranged in a spiral around the stem. Axillary buds grow from the axils of the leaves and these give rise to branches or flowers. A terminal bud lies at the tip of the stem. 

     Each leaf of the balsam is a flat green structure with a toothed or serrated edge. The tip is pointed. The leaf stalk, or petiole, extends through the leaf blade, or lamina, to form the mid rib, also known as the main vein. Branch veins with little veinlets branch out from the mid rib to form a net venation. 

     The flowers are attached to the axils of the leaves by pedicles, or flower stalks. The flower is the reproductive organ of the plant. It has five petals which may be white, pink, red or purple in colour. When it is fertilized, it develops into a fruit which contains seeds. The fruit is green and covered with small The seeds are enclosed in the fruit. They are green when young and dark brown when ripe. The ripe fruit disperses its seeds by means of an explosive mechanism. 

ANNUALS, BIENNIALS AND PERENNIALS

     Flowering plants can be classified into three groups on the basis of the nature of their life cycle and their span of life. These groups are the annuals, biennials and perennials. 

          ANNUALS

     An annual is a plant which completes its entire life cycle and dies within one growing season which may be a few months or at most one year. After the seed germinates, the plant grows and produces flowers which in turn produces fruits and seeds. Once the seed has been produced, the rest of the plant dies. Many of the world's useful plants are annuals. Examples of annuals include cereal plants like rice, wheat and maize, bean and pea plants, flax, jute, okro (lady's fingers) and sunflower. 

          BIENNIALS

     A biennial is a plant which passes through two different phases in one life cycle. In general, it has a longer life span than an annual, the life span being approximately two years, i.e. a year for each phase. During the first phase, biennials such as the carrot attain their full vegetative growth and develop large storage organs. Food stored in these organs is made use of in the second phase when the plant sends up a leafy shoot bearing flowers, fruits and seeds. After this the plant dies. If adverse conditions prevail after the first phase, the vegetative shoot dies down. When favourable conditions return, the storage organs produce new vegetative shoots. Many garden food plants are common examples of biennials, e.g radish, cabbage and turnip. Usually these plants are harvested for food immediately after they complete their first phase of growth. 

          PERENNIALS

     Perennials are trees, shrubs and herbs which continue to grow from year to year, producing flowers, fruits and seeds for manyThey can be divided into two groups— herbaceous and woody perennials. In herbaceous perennials, the aerial parts of the plants may die down every year at the end of the favourable season after producing flowers and seeds. Most herbaceous perennials persist by means of underground stems and roots e.g. corms, bulbs, tubers and rhizomes. These usually contain a store of food which is used for the production of new flowering shoots when the favourable season returns. Usually the terminal or lateral (axillary) buds on these underground organs develop to form new aerial shoots. Examples of herbaceous perennials are lilies, dahlia, water chestnut, onion, garlic and ginger. 

     Woody perennials are plants such as trees, shrubs and vines, in which the aerial stems and branches persist and grow from year to year. Trees growing in temperate countries shed their leaves with the approach of winter and are said to be deciduous. A number of trees in the tropics also behave in a similar manner. However, most trees growing in the tropics never shed all their leaves at one and the same time and are said to be evergreen. Examples of woody perennials are the flamboyant (a deciduous tree) and the Bougainvillea ( an evergreen shrub). 

          THE ROOT

     The root is the descending portion of the axis of the plant. It develops from the radicle of the embryo. The radicle lengthens to form the primary root which persists and continues to grow as the tap root, or main root. The tap root produces lateral branches which are known as secondary roots, and these in turn produce tertiary roots. The older and longer roots are situated away from the root tip while the younger and shorter ones are closer to it. The root system just described is a tap root system and the roots are known as true roots. A tap root system may be regarded as characteristics of dicotyledons.If the primary root does not develop any further or soon perishes, it is replaced by a cluster of thin roots which develop from the base of the stem. These roots which are approximately of equal length and thickness with no distinguishable main roots, are known as fibrous roots. They make up a fibrous root system which is characteristics of monocotyledons.