Mesic Adaptation in Plants
The plants which require moderate amount of water (mesic conditions) are known as mesophytic plants. The soil in which they grow is neither very wet nor dry. These plants are usually found in the plants and gardens. Rose, peepal, mango, sunflower, goldmohur, etc. are common examples of mesophytic plants.
Many plants and animals found in tropical forests of India and South-East Asia show adaptations to terrestrial life. The orchid plant (Vanda) is a very good example which adapts itself suitably to changes in temperature and humidity. It is an epiphyte and a native to tropical forests. The stem of the orchid stores water and leaves are specially modified to keep water in and dryness out. The roots of this plant are wandering or hanging in air which absorb moisture from the rains or humid air.
Xeric Adaptation in Plants
Plants which live in dry conditions are known as xerophytic plants (xero means dry). The scarcity of water may be of two types: (1) physical in which there is actual shortage of water and (2) physiological in which water is present but the plants are not able to absorb it because of excess of salts or very low temperature of the soil.
Xerophytic plants are modified in such a way that lesser amount of water is lost from various parts. For reducing transpiration, the leaves of xerophytic plants have lesser number of stomata, which are sunken and hairy. Their outer layer (-epidermis) is thick with cuticle. Vascular tissues are modified accordingly to reduce water loss from the body. The cactus plant is a good example where the following adaptation can be seen.
1. Leaves are modified into spines or scales. T5his helps in reducing the loss of water from the leaf surface by transpiration.
2. The steam and leaf surfaces have thick cuticle with a covering of waxy substance.
3. They have sunken stomata.
4. The stem of the plant is mostly spongy and succulent which helps in storage of water.
5. Their seeds remain dormant during unfavourable periods. They germinate upon the arrival of favourable conditions.
In Opuntia (cactus) stem becomes fleshy, green and leaf-like. This adaptation is called phyllociade.