Water plants and desert plants
Plants in the water
water plants in a pond
These plants grow in water. Water is available to them in large quantities. Enough air is not available to the roots.
Examples of water plants
Hydrilla, pista and lotus, etc., these are the water plants.
1) Some plants are completely submerged under the water. Their roots are also fixed in the soil under the water. Such plants are called submerged plants. – Hydrilla, utricularia, vallisneria.
2) Some plants float on water. Such plants are called free floating plants. – Pista, eichhornia.
3) The leaves and the flowers of some plants float on water but the roots are attached to the soil at the bottom of the pond. - Nymphea (lotus).
Characteristics of water plants
1) Water plants have a weak stem and the weight of leaves and flowers is borne by the water.
2) There is no need to absorb water by roots. The only function of the root is to fix the plant in the soil.
3) Air spaces for respiration are found in the stem and roots. They are spongy.
4) Dissected leaves are present in submerged water plants to allow free flow of water. Leaf stalks contain air spaces.
5) The air spaces allow free flow of air and also keeps the plant floating.
6) The plant is balanced with the help of the roots. The roots also help the plants to float on water.
7) The leaves of water plants do not get wet as the upper surface of the leaf is coated with wax. Waxy coating of the leaf does not allow the water to enter the leaf through stomata.
The plants which live in deserts are called Xerophytes.
Examples- opuntia, cactus are the desert plants.
The rainfall is very less in deserts. The mineral nutrients are not absorbed by the plants because of scarcity of water. Still some plants modify their structure and are able to live in adverse conditions of deserts.
Opuntia is able to survive in deserts
1) It has deep rooted system which reaches great depths to absorb water.
2) The stem is modified in to a green flattened structure. The leaves are reduced to spines to prevent loss of water through transpiration. Some times leaves are modified to scales to save the little amount of water available to them.
3) As the leaves are modified in to spines the stem has to prepare the food now. The stem is a flat, broad, and green structure which prepares the food.
4) to avoid transpiration Xerophytes have different mechanisms like –
a) A thick covering known as cuticle is present on the stem, which does not allow transpiration.
b) The plant bodies are small to reduce transpiration. Thus Xerophytes have modified their structures suitably to conserve water.