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· We lifted a plant.
Let us take a look at it.
· What do we see?
· A green part, in the air - the stem.
· A grey part, in the soil - the roots.
· Between the stem and the roots - the collar, or crown.
Let us look at the roots.
They are divided into smaller roots and rootless.
· The smallest roots are called rootless.
The rootless come at the end of the roots.
The plant and its
roots
· There are parts of the rootlet which perhaps you cannot see, because they are too small or because they have remained in the ground.
· To see them better, make another seed germinate. Put a bean seed in the earth. After three days lift it carefully. The root should be about as long as a match. To see better you need a lens. Perhaps your teacher can lend you one.
What do you see?
· At the tip of the rootlet there is the root- cap.
The root- cap is small and hard.
Its purpose is to enable the
rootlet to penetrate the soil.
· On the rootlet there are absorptive hairs.
· Above the absorptive hairs there is a dark, hard part.
This is the oldest part of the root.
It does not take in
food.
It does not absorb food.
The absorptive hairs of the rootlet
· There are very many of these hairs, but they are very thin, very short and very fragile.
You may not be able to see them.
These hairs are like those on your head, but they are very short, and thin, and there are very many of them.
These hairs are called absorptive hairs because they take from the soil the food which the plant needs in order to live and grow.
They are like little mouths which take in food for the plant.
The hairs absorb food.
A rootlet
A plant feeds only through the absorptive hairs on its rootless.
Let us cut a root with a knife.
What do we see?
· On the outside is the skin.
· Under the skin is a hard, moist part, where the sap flows in little tubes called vessels that make up the vascular system.
Through this system the sap flows.
In man blood flows through
veins and other vessels.
In the plant sap flows through the vessels.
Vessels carry sap in the root
What are the foods which the plant takes from the soil?
They are mineral salts.
· In the soil, mixed with it, are mineral salts.
These mineral salts are the plant's food.
The mineral salts
and the water are absorbed by the root hairs.
They become sap in the plant.
When there are plenty of mineral salts in the soil, the soil is rich. The plant grows well.
· When there are not many mineral salts in the soil, the soil is poor. The plant grows badly.
The soil can be given mineral salts in the form of fertilizers and manure.
· The roots of a maize plant, a millet plant and a rice plant are alike.
· The roots of a mango tree, an orange tree and a lemon tree are alike.
· The roots of maize, millet and rice are not like those of the mango tree, the orange tree and the lemon tree.
· Different plants have different roots.
Some plants have small, thin roots, all of the same length.
· These roots form a tuft, as for instance the roots of onion, rice, millet, maize.
Rice has fibrous roots
· A plant that has many small roots of the same length, the same thickness, the same shape, has fibrous roots.
Some plants have roots that are shallow and long.
· Creeping roots do not go deep into the soil.
· These roots go a long way from the base of the plant.
They cover a large area.
They have to find in a small depth
of earth the food necessary for the life of the plant.
Many trees have
creeping roots.
Creeping roots
· A plant that has shallow, very long roots has creeping roots.
Some plants have only one root, very thick, deep, straight, called a tap- root.
· Smaller roots grow on this thick root; they are called rootless.
· Tap-roots go deep into the soil.
They cannot penetrate soil that is too hard.
Types of tap root
· Cotton, coffee, cocoa, okra, carrots, papayas all have a root that goes deep into the soil, is very thick and straight.
They have a tap- root.
Some plants have very thick roots.
· These roots store up food.
· These roots are thick because they have taken up a lot of food from the soil.
The food is stored up in order to feed the whole plant.
The
plant is said to have built up reserves.
For example, cassava.
Cassava roots
· A plant that stores up reserves in thick roots has tuberous roots.
In some plants roots start from the stem above the soil, that is, above the collar, and afterwards go down into the earth.
· Adventitious roots grow above the collar.
For example, mangrove, bamboo, maize and rice all have adventitious roots.
A rice plant
· Soil put around the collar helps adventitious roots to grow; the plant is earthed up.
· A plant with roots on the stems has adventitious roots.
Earthing up encourages
adventitious roots to
develop
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