Plant, its parts and their functions

PLANT, ITS PARTS AND THEIR FUNCTIONS

Plants are highly important sources of food for man. They supply us with clothing and many other

things as well. Plants are grown and used for many purposes and as scientists continue their work

new uses of plants will be found.

The principal parts of a plant are: 1) the root system, 2) the stems and leaves, 3) the reproductive

part made up of flowers, fruits and seeds.

The roots grow downward into the soil and have two main functions- to absorb plant nutrients

and water from the soil and to anchor the plant. As to stems and leaves, they are usually above the

ground. The food used in growth by green plants is manufactured in the leaves from the raw materials

taken from the soil and air. This process is known as photosynthesis. To support the leaves and to

connect them with the roots are the main functions of the stem.

Each flowering plant has leaves. A typical leaf consists of a green, broad, thin portion, the blade,

which contains a system of vascular tubes called veins. The latter serve as channels for the distribution

of water and dissolved substances and for removing a part of the food which is manufactured in the

leaves for the use by the plant.

The shape and the position of the leaves vary to a considerable extent with the species. Leaves

may be borne on a leaf stem, or attached directly to the plant. They may be compound as with clovers

and potatoes, or simple as in the case of the poplar tree.

A flower is the part of the plant where seeds are produced. Thus, to produce seeds the plant must

have flowers.

A seed consists of an embryo, and one or more seed coats.

All parts of a plant must be developed well and proportionally enough to function properly. If

conditions for plant growth are bad, the plant will be too weak to develop its parts well.

ROOTS AND RHlZOMES

Roots are one of the three kinds of organs that most plants must have in order to grow. Rhizome

is a horizontal underground stem which looks like a root. It serves as a special organ for storing food.

Some medicinal plants (Valerian, Althea, Ginseng etc.) are very valuable by their roots and rhizomes

that are used in preparing medicinal forms. Roots and rhizomes are subterranean organs of plants that

hold the plants in place and supply them with water and nourishing salts from the soil.

It is well known that roots and rhizomes are easily recognized by their appearance, colour, odour and

taste as wel1 as by the structure of transverse section. Roots and rhizomes are gathered, washed or

freed from earth, crushed or cut into pieces and dried corresponding to each drug dispensary form.

Roots with different forms have special names. Roots that are formed first and grow directly from

the stem are called primary roots. A primary root that grows much longer than any of its branches is

called a tap-root. Sometimes tap-roots grow very thick and store up food for the rest of a plant. These

are fleshy roots or tubers that can be seen in carrot, radish etc. A cluster of thick primary roots are

called fascicled roots. Roots may grow on the stem or in other unusual places. They are known as

adventitious roots. Adventitious roots grow on plants which need extra support for their stems.

СLASSIFICATION OF PLANTS

There are four important different groups of plants.

Thallus plants, or Thallophytes, are the lowest and simplest of all plants. The group includes the onecelled bacteria, the algae, and the fungi, like the molds that are often seen growing on bread and

cheese. Bacteria can only be seen with the microscope, but some of the seaweeds are hundreds of feet

long.

Another group of relatively simple plants includes the mosses, lichens and liverworts that are found

in forests. Moss Plants, or Bryophytes, have no true roots or stems. Instead of leaves they have green,

leaflike scales. Most plants belonging to this division are quite small.

A third group of plants includes the fern, quillworts, and club mosses. They are Fernlike Plants or

Pteridophytes. These plants have neither flowers nor seeds, but they are divided into distinct parts,

including roots, stems and leaves.

Most of the plants we know belong to the group of plants called Seed Plants or Spermatophytes.

They have the most complex structures of all plants. These are the only plants that have flowers and

reproduce by fertilization with pollen. Such plants include our common grasses, vegetables, most

trees, shrubs, flowers and many others