Tuesday, December 2, 2008

ADAPTATIONS IN HYDROPHYTES AND XEROPHYTES

Hydrophytes (Adaptations in plants to aquatic environment)
The plants which are growing in water partially or completely are known as aquatic plants or hydrophytes. Water may be freshwater or saline. Plants which grow in fresh water bodies like ponds, lakes, pools, streams, rivers etc.are known as freshwater plants, and those growing in salt water are known as saltwater plants or marine plants. The free-floating, on-vascular hydrophytes constitute phytoplanktons.
The aquatic plants show the following adaptations.
Morphological adaptations
1. Roots may completely be lacking (wolffia, utricularia) or feebly developed (hydrilla).
2. Root hairs are absent (lemna) or feebly developed.
3. Roots caps may be absent or root pockets are present (eichornia).
4. Roots are generally fibrous type and adventitious, unbranched or sparsely branched.
5. The stem is long, slender, weak, spongy and flexible type in submerged hydrophytes.
6. The stem is short, stoloniferous, thick, and spongy, with extensive parenchyma in free floating plants.
7. The leaves may arrange in alternate phyllotaxy (potamogeton) or opposite (cabwoman) or whorled (hydrilla).
8. Stomata are present on the upper epidermis which is in contact with air and gaseous exchange takes place through this stomata and lower surface is in touch with water.
9. The upper leaf surface in floating leaves are coated with wax to prevent wilting.
10. The of many partially submerged plants show hetrophylly (presence of different types of leaves).
E.g. ranunculus aquatilis
11. The entire plant body covered with mucilage.
12. The flowers and seeds are less abundant.
13. Reproduction is mainly by vegetative methods.
Anatomical adaptations
1. Excessive development of parenchyma and elaborate system of arenchyma (air space)
2. Poor development of vascular and mechanical tissues.
3. Cuticle absent or poorly developed
4. Stomata are completely absent in submerged leaves.]
5. Chlorophyll found in all the tissues.
6. Mucilage canals and mucilage cells are present which secrete mucilage to protect the plant body.
7. The reserve food is in the form of starch grains which occur in cortex and pith.
8. Cystoliths (sclereids) of various shapes are seen in leaves and other tissues.
Xerophytes (Adaptations to dry environment)

The plants which are growing in xeric (dry) environment (habitat) are called Xerophytes. Deserts are the best examples for xeric environment, where plant face inadequate water and excessive transpiration .xerophytes are classified into the following three categories-Ephemerals [the plants complete their life cycle within a short period. they also called “drought escapers” or “drought evaders”], Succulents [these plants have succulent, fleshy organs, to store to store high amount of water accumulated during rainy seasons. these xerophytes suffer dryness only in external environment],true xerophytes[these plants which are able to live under extreme dry conditions and high temperature].the xerophytes show the following adaptations.
Morphological adaptations
1. Stem shows stunted growth
2. Certain plants have under ground stem to tide over dry season.
3. Plants like acacia, zizyphus etc .have very hard ,woody stem with thick bark.
4. In many plants the leaves are reduced to scaly or spiny e.g.ruscus, asparagus etc.
5. Many plants have very small and narrow leaf blade to reduce the transpiration area.
6. Some plants have shining leaf surface to reflect light. E.g.nerium odorum.
7. In certain plant leaves leaves are very thick and leathery to reduce transpiration. E.g.calotropis procera
8. Many plants have waxy coating on the upper surface of leaves.
9. Folded type leaves are seen in some of the grasses to protect the
10. In non-succulent plants root system is several times larger than the aerial portion.
Anatomical adaptations
1. Presence of thick cuticle on the upper surface of leaves.
2. The epidermal cells are thick walled.
3. Multiple epidermal layers are seen on both upper and lower surface of leaves.
4. Stomata are reduced in numbers and are sunken type.
5. The stomata pits are filled with number of hairs.
6. Thick walled sclerenchyma cells are seen in the hypodermis. E.g. pinus needle
7. Few spongy parenchyma cells with small inter cellular spaces.
8. Presence of many layered palisade parenchyma
9. The cells are relatively smaller in size and vacuoles are small.
10. Well developed vascular tissues are present.
Materials and methods
Materials:-
Xerophytes root, stem.
Hydrophytes stem, leaf, and root
Methods:-
Take the transverse of the stem and root mounded with glycerin after
Mounded with glycerin after the stained.
Observed prepared slide through microscope.

2 comments:

Tanaya said...

Perfect study material. Im a studnt of c.u 3rd yr botany honours

Tanaya said...

Happy to get such a good material for study..jst b4 the final xam