Xerophyte plants have adapted in order to obtain the correct amount of water to carry out the important processes that allow the plant to survive and grow successful in its environment. The succulent plants illustrate clearly the principle that unrelated plants, under similar environmental conditions, may develop striking similarities in external form. Stomata are found on the stem, and are very important as this is how gases are obtained for necessary cellular processes. Ø In many plants, the stem is covered with dense hairs Example: Calotropis. The xerophytes are classified into three categories. In whales cervical vertebrae are coalesced to form a solid compressed mass of bone. In Trapa and Eichhornia petioles are swollen and spongy.
Therefore, the coronoid process of mandible is reduced. The root system is well developed, extensive and much branched. An adaptation that is absent in xerophytes and mesophytes, but is found in hydrophytes, is a hollow stem. A Succulents with fleshy stem: In xerophytes with succulent stem, the leaves are reduce to spines or are altogether absent. These roots are called pneumatophores and they possess breathing pores for gaseous exchange.
The integument of aquatic animals is either rich in mucous glands or is protected with scales. An evolutionary strategy employed by desert xerophytes is to reduce the rate of seed germination. Rooted with floating leaves: In certain hydrophytes such as Nymphaea, Nelumbo, Trapa, Marsilea, and Aponogeton, the roots are fixed in mud but leaves have long petioles which keep them floating on the water surface. Other xerophytes may have their leaves compacted at the base, as in a , which may be smaller than the plant's flower. Xerophytes in heat are constantly at risk of evaporation, so the silver colour helps prevent and decrease water loss. Important plants found in these forests are conifers, Myrtaceae, Hymenophyllaceae.
Lesson Summary Specialized adaptations allow plants to survive in all types of extreme environments. Rolling of leaves is observed in some xerophytes like Ammophile where the stomata are directed inwards. Such drought-loving plants are known as xerophytes and possess several types of structural and functional modifications which result in an ability both to draw water from the soil and to retain it in the plant tissues. Some amphibians like spade- foot toads Scaphiopus an estimate for eight or nine months in an underground cell lined with a gelatinous substance that reduces evaporative losses through the skin. Finally he evaluates various ideas about progress in evolution, denying that selection will bring about the kind of progress that some have suggested.
They may or may not be rooted in the soil. Most of these plants are small, roundish, dense shrubs represented by species of , some inconspicuous , a few and some grasses. In addition a waxy coating on the surface of the leaf may also occur e. Reproductive characters Classification of plants based on water relation Warming, 1990 1. These plants control the excessive loss of water during transpiration by reducing total transpiring surface, 3.
Mucilage cells and muscle age canals are present which secrete mucilage to protect the plant body from decay under water. Xerophytic plants exhibit a diversity of specialized adaptations to survive in such water-limiting conditions. In dry environments, a typical plant would evaporate water faster than the rate of water uptake from the soil, leading to and even death. Since water makes up a large proportion of the bodies of plants and animals 70 to 90% water in protoplasm , it affects all life processes directly. The amount of water necessary to maintain life varies from species to species. By reducing leaves to spines on some xerophytes, this greatly reduces the surface area of the leaf, which greatly reduces the amount of transpiration, helping assist in reducing water loss.
Certain plants have under ground stem to tide over dry season. Ø Roots are not required for the absorption of water or nutrients. The wilting of leaves is a reversible process, however, abscission is irreversible. This adaptation probably helps to prevent pulling away of the protoplasm from the cell walls under conditions of excessive drought and desiccation. In some plants, surfaces of stems and leaves develop characteristic ridges and furrows or pits. The plants show luxuriant growth and they are found in several storeys.
Fluted stems, such as those of giant cactus Carnegiea gigantea store huge amount of water and undergo characteristic expansion and contraction during moist and dry periods, respectively. The aquatic environment is subject to water movements ranging from small vertical circulation to strong currents. Ø They are usually short sized plants in which the flowering and fruiting occur before the next unfavourable season. Its cells are extremely thin walled. B fruit to attract animals for dispersal. Under high light, it is unfavourable to channel extra light into photosynthesis because excessive light may cause damage to the plant proteins.
A developed xylem system also allows for transpiration pull to occur, and this is an essential process which must occur in mesophytes, so water can reach the leaves and so the plant is able to carry out photosynthesis, and therefore its life processes, in order to survive. Stomata may be present in pits i. Root hairs and root caps are well developed in Opuntia. It also varies with the stage in the life cycle of a single species. This makes the stems swollen and fleshy Figs. This sequence is possible only if the biotic factors are not allowed to affect the vegetation to a major degree. During desiccation, the levels of the sugars sucrose, raffinose, and galactinol increase; they may have a crucial role in protecting the cells against damage caused by and oxidative stress.