III B.Sc PRACTICAL PAPER-VII

STUDENTS CORNER AND LIGHT OF KNOWLEDGE UPDATED

PLANT PHYSIOLOGY - II & ECOLOGY II 

MAJOR EXPERIMENTS

EVOLUTION OF OXYGEN DURING PHOTOSYNTHESIS BY THE BUBBLE COUNT METHOD

Aim: To determine the rate of photosynthesis by the bubble count method. 
Requirements:
 Trough, Water, Funnel, Test tube, Hydrilla twigs and CaC0_3.

Procedure: A healthy Hydrilla twig is selected and one end of it is cut slant wise under water. The trough is then completely filled with sufficient water so as to immerse the funnel completely. A test tube completely filled with water is then placed in the inverted funnel with its cut end for sometime. When a steady stream of bubbles is given out the readings are noted for 3 trials. The set up is then placed in diffused light and the readings for 3 trials noted.

Observation: Air bubbles begin to come out from the cut end of the twig. The air bubbles collects at the top of the test tube, as a water level falls down in the test tube.

Inference: Photosynthesis is an aerobic process occurring in green plants makes use of 2 raw materials CO₂ and water. To synthesize organic compounds like sugar in presence of light absorbing pigments, making use of solar radiation as a source of energy. The process releases molecular oxygen as a byproduct. The aquatic plants like Hydrilla makes use of CO₂ dissolved in water. The oxygen liberated due to photooxidation of water is light reaction. 

NOTE:

1. It is sufficient when only one Hydrilla twig is taken.

2. The slantwise cut should be made under water.

3. Readings can be noted under different intensities of light
. 

SEPARATION OF CHLOROPHYLL  PIGMENTS  BY

PAPER CHROMATOGRAPHY AND CALCULATION OF Rf VALUES

Aim: To separate the different chlorophyll pigments and calculate their Rf values.

Requirements:

 Fresh leaves of betel, Tecoma, Spinach, Grass, Neem, 85% acetone, Sand,

CaC03, Petroleum ether, Acetone (100 ml of petroleum ether: 12 ml of 85 acetone), Hair drier, Chromatography tube, Piece of cloth.

Procedure: 10 gms. Of leaves of any type are selected and their mid - ribs removed. They are then ground into a paste using about 5 to 10 ml of 85 acetone, (with a pinch of Ca^C03) and a few grains of sand. The ground material is then mixed with 30 ml of 85 acetone and filtered on a piece of cloth and the extract collected in a beaker. The whatmann filter paper is cut to the required size and a pencil line drawn at a distance of 2.5 ems from the base of the filter paper. A loading spot is marked in the middle of this line. The loading of the chlorophyll extract can be done with a capillary tube, drop by drop and dried soon after. About 15 - 20 drops of the extract is fed, until the spot

becomes concentrated.

The chromatography tube is then filled with the solvent mixture (the solvent mixture

consists of 85% acetone and petroleum ether in the ratio of 12 ml: 100 ml as per requirement). The tube is allowed to be saturated with the vapours of the solvent mixture. The loaded whatmann paper is then introduced in such a way that only the base of the paper is in contact with the solvent mixture. The solvent is allowed to rise up to the maximum level after which the paper is removed and dried.

The coloured bands of the 4 pigments are marked with a pencil immediately. The distance from the pencil line on the paper to the point that the solvent has moved up gives the solvent front. Similarly the distance from the pencil line to the middle of each band gives the solute front.

Rf value of the pigment = Distance from the pencil line to the centre of each band (solute front)

                                   Distance from the pencil line to the distance traveled by solvent(solvent front)

Result:

Inference:

NOTE:

1. Freshly collected leaves should be used.

2. The loading spot should be as small as possible and using a narrow capillary tube.

3.     The chromatography tube should be saturated with the solvent vapours before the insertion of the filter paper. 

4.      The filter paper should be erect and only the lower edge should be touching the solvent.

5. For the erect suspension of the filter paper the cord can be fitted with a hook.

6.     The solvent can be 80 ml of petroleum ether: 20 ml. of 85% acetone instead of 100 ml. petroleum ether: 12 ml. of 85% acetone. (Benzene: Acetone, 85 : 15 can also be used).

7.     The four pigments coloured band will be in the following order (from top to the bottom): carotenes (orange yellow), xanthophylls (yellow, one or more bands), chlorophyll a (blue green) and chlorophyll b (yellow green).

GANONG'S RESPIROMETER TO DEMONSTRATE THE EVOLUTION OF CARBON DIOXIDE DURING RESPIRATION

Aim: To demonstrate the evolution of carbon - di - oxide during respiration by germinating seeds.

Requirements:

 Ganong's respirometer, Stand, Beaker, Germinating green gram, Salt, Water, KOH, Cotton

Procedure: fix the Ganong's respirometer to stand and place a piece of moist cotton in the bulb. Fill the bulb with sufficient amount of germinating seeds with the seed coats removed. Fix the stopper of the bulb in such a way that the two openings of the stopper and bulb coincide. Pour concentrated salt solution through the levelling tube and see that the levels are equalized both in the graduated and leveling tubes. Turn the stopper of the bulb so as to cut out the supply of air from outside. Leave the set up aside for about an hour or so after which a strong solution of KOH is poured into the levelling tube.

Result:

Inference: Carbon - di - oxide liberated within the bulb during the respiration of seeds is absorbed by KOH solution. A vacuum is created there. This leads to the ingrease in the level of salt solution in the graduated tube. The oxygen gas present in the bulb is consumed by the respiring seeds & carbon - di - oxides is released to its place.

Volume of CO₂ liberated == R.Q. Here it is  = 1 (unity).carbohydrates have the R.Q = 1

Volume of 02 consumed

NOTE:

1. Germinating green gram seeds give good results.

2. Take sufficient quantity of seeds to ensure evolution of CO₂

MEASUREMENT OF R.Q. USIMG MAC - DOUGHAL'S RESPIROSCOPE

Aim: To measure the respiratory quotient by using a pair of respiroscope (Mac Doughal' s)

Requirements:

 A pair of respiroscope, Stand, Thermometer, Water, Germinating seeds (green gram)

Procedure: Place the pair of respiroscopes on a vertical wooden stand. In the upper wider portions of the two test tubes take equal quantities of the given material (green gram). In one of the tubes, say B. a small glass tube containing pellets of KOH is hung from the top. The lower ends of both the tubes are dipped below the surface of water present in the beakers.

The stop cocks of the tubes are opened one by one. Air is sucked out with the help of rubber tubing till water rises to a predetermined mark in the graduated tube. The initial levels are kept the same in both the tubes. The thermometer indicates the temperature at which respiration proceeds.

The stop cocks are closed immediately and the tubes made air - tight. After about half an hour the levels in the two tubes are noted. In tube B there is normally a rise in the level because carbom - di - oxide liberated during respiration is absorbed by KOH. This rise in level, therefore indicates the total amount of carbon - di - oxide liberated and is denoted as V 2· as we know, in respiration O₂ and CO₂ only are involved, it may be taken for granted that the volumes of the two gases are equal. Then replace A by a new respiroscope tube (or the same tube can be used after washing) without seeds and dip it into pyrogallate of potash (instead of water). Soon the solution as it absorbs O₂ rises to the same extent as in B. it may therefore be concluded that in respiration the volume of CO₂ given out is equal to the volume of O₂ absorbed.

The R.Q. = Volume of CO₂ liberated              Rise in the level of H₂0 in tube B            = 1

                     Volume of O₂ absorbed             Volume of oxygen (same as above) 

Observation:

Inference: The rise in the water is due to the absorption of CO₂ by the KOH. There is no rise in B as there is no vaccum. Therefore B shows that the total volume of air in it is constant. In the tube A, the volume of O₂ used is approximately equal to the amount of CO₂ liberated.

KHUNE'S TUBE TO DEMONSTRATE ALCOHOLIC FERMENTATION 

Aim: To demonstrate alcoholic fermentation.

Principle: The breakdown of cell fuels such as glucose, without oxygen is anaerobic respiration. Alcoholic fermentation is one such process. It produces both ethanol and carbon dioxide.

Materials required:

 Kuhne's fermentation tube, Glucose, Bakers' yeast, Water, Cotton

Procedure: A 10 solution of glucose in water is prepared. A small quantity of bakers' yeast is dissolved in a little water till a creamy mixture is formed. This i~ then mixed with the glucose solution. The Khune's fermentation is tube is now filled with the glucose + yeast mixture in such a way that the vertical limb is completely full, and the bulb only partially full. The opening of the bulb only plugged with cotton and the apparatus is left undisturbed in a warm place for about 24 hours.

Result: Bubbles of gas collect in the closed limb of the vessel and the level of the solution goes down. if a small piece of KOH is put into the tube, the level will rise again. As fermentation proceeds the smell of alcohol can easily be detected.

Inference: Fermentation releases carbon dioxide which is absorbed by the KOH, hence the rise in the level.

MINOR EXPERIMENTS:

GANONG'S COLOURED LIGHT SCREEN EXPERIMENT 

Aim: To determine the effects of different wavelength of light on photosynthesis. 
Requirements:

 A potted plant, Ganong's light box ( Ganong's light box with removable lid in which the glass plates of different colours can be fitted), Beaker, 70 alcohol, KI solution, Test tube, Spirit lamp

Procedure: Place a potted plant in dark for about 48 hours so that the leaves becomes free of starch. Fix the glass plates of different colour, namely blue, green & red in the light box. Now insert a leaf for de starched plant in the box. Keep the apparatus in bright sunlight for few hours. After a definite period, detach the leaf from the box & boil in 10 alcohol till it decolourises. Stain it with KI and observe.

Observations: In portion of leaf covered with red glass plate, stained dark blue, the portion of the leaf covered with blue light stained light blue & the portion of leaf with green light remained almost unstained.

Inference: This indicates the red light is most effective, blue light is less effective and the photosynthesis nearly stopped in green light.

MOHL'S HAL LEAF EXPERIMENT Aim: Experiment to show that CO₂ is necessary for photosynthesis. 
Requirements:

 Potted plant, Conical flask, KOH solution, Split cork, Iodine solution

Procedure: A healthy leaved potted plant is selected. It is kept in darkness for a day or two to destarch the leaves. A leaf is inserted in to a wide mouthed bottle or flask through a split cork. 
20%  KOH solution is taken in the flask or bottle. The portion of the leaf outside the bottle or flask has an access for atmospheric CO₂. The apparatus is kept under sun for several hours.

Observations: The portion of the leaf outside the bottle turns blue sho\ying the presence of starch. The portion of the leaf which was enclosed within the bottle does not stain blue. Inference: This clearly indicates that C02 is essential for photosynthesis because the portion inside the bottle did not get C02 as it absorbed by KOH solution.

CLINOSTAT EXPERIMENT

Aim: To demonstrate the effect of gravity (geotropism) in plants with the help of horizontal clinostat.

Procedure: The clinostat consists of a round disc attached by means of an axis to a clock - work arrangement. The disc can be made to rotate fast or slow. Fix a potted plant to the rod fitted to the centre of the disc in a horizontal position & the clock work is started. Now observe the bending of the axis under the following condition.

1.     If the instrument is not working ( when the clock work is stopped that is if disc is not

rotating) the stem apex or shoot will bend and grow upward because stem is negatively geotropic & the root although not visible because of the soil will bend downward as roots are positively geotropic.

2.     When the clock work is on if the disc is slowly rotating, with the rate of about 1 to 4 rotations per hour, the plant will continue to grow horizontally (normally i.e straight) because each side of the axis is inturn directed downwards, because the gravitational force or the stimulus of gravity acts equally on all the sides of the stem tip. (It will not result I the unequal growth in the apex & the apex growth of). Moreover, the stem will not be in anyone position long enough for a negative response to occur.

3.     If the disc is fast rotating, the stem apex will bend obliquely outwards due to the development of centrifugal force.

Expected result: When the clockwork is on the stem tip as well as the root tip grows straight

When the clockwork is off the stem tip grows upwards showing negative geotropism and

root tip grows downwards showing the positive geotropism.

Inference: Thus geotropism in plants can be demonstrated by the clinostat
.

POROUS CLAY FUNNEL

Aim: To demonstrate positive hydrotropism of roots by porous clay funnel experiment. Requirements:

Porous clay funnel, Conical flask, Saw dust, Germinating seeds, Water

Procedure: A porous clay funnel ( a clay funnel with vents or pores around it) is taken & soil & sawdust is put into it. A few seeds are sown in it and the funnel is placed on the conical flask filled with water. The apparatus is kept aside for some days. The porous wall of the funnel becomes saturated with water.

Expected result: As the seedlings germinate, the roots at first come out through lower end of the funnel, but later due to the lack of the space the newer roots start emerging out of the vent or the pores & grow downwards towards the water. The roots grow hanging on the moist walls of the funnel, thus showing positive hydrotrophic movement.

Inference: thus the porous clay funnel can be used to demonstrate hydrotropism.

Note: Tropic movement is shown by any bilaterally symmetrical organ of a plant like root & atem to an external stimulus, such as gravitation force, water, sunlight etc. They are called respectively as geotropism, Hydrotropism & heliotropism. 

Loranthus (Loranthaceae):

It is a partial stem parasite. The stem of cuscuta produces adventitious roots as haustorial roots. They penetrate through the epidermis of the host stem into its phloem. The haustorial roots draw food materials from the host phloem into it. Loranthus has green leaves and hence can photosynthesize and prepare its own food materials, thus it is partially autotrophic too. Its parasitic nature is thus secondary.

Striga Striga is a partial root parasite. It parasitizes the roots of grasses growing near by. The roots of the host are attached towards the parasite for parasitization.

Balanophora It is a total root parasite, usually parasitizing some of the very large trees in the rain forest . its stem is rhizomatous, underground, white in colour, without chlorophyll. It produces certain secretions to attract the roots of the host tree towards it. It develops a direct contact with the host root and establishes connection with the host vascular bundle. The rhizomatous portion of balanophora often produces white scale leaves on an erect scape, which emerges out of the soil like a white cottony button. It is the inflorescence, found at the surface of the soil exposed.

Nepenthes / Pitcher plant

Nepenthes is a insectivorous plant. The entire leaf including the leaf blase is involved in the modification. The leaf base is modified into broad leaf - like structure, the petiole into wiery tendril, the leaf lamina into a pitcher and the leaf tip into a lid. The whole structure is meant for trapping insects and digesting them to obtain a part of nitrogen requirement. The inner surface of the flask like pitcher produces hanging digestive hairs which produce the digestive juice that is found half filled in the pitcher.
Utricularia - Bladder wort

This is an insectivorous plant. It is a rootless submerged plant, commonly seen in ponds and tanks. The plant produces highly segmented green leaves. Some of the segments of the leaves are modified into insect trapping bladders. The bladder has a trap door which allows the small aquatic insects to enter and trap them. The insect body is digested within the bladder by the juice secreted by the digestive glands located on the inner surface of the bladder.

Drosera - Sun dew

Drosera is an insectivorous plant. The spoon like leaves, with the upper surface covered by numerous glandular hairs called tentacles. These secrete a sticky fluid that shines in sunlight like dew drops. Small insects attracted by shining drops land on the leaves especially on the tentacles. Immediately the tentacles bend down on the entangled insect cover it & digest it.

HYDROPHYTES

Hydrilla (Hydrocharitaceae):

It is a anchored - submerged hydrophyte, found in ponds, tanks and slow moving water. The plant is fixed to the substratum by adventitious roots. The plant is covered over by mucilage which protects against epiphytic growth.

The stem is herbaceous, green, spongy, fistular and profusely branched. The leaves are (elodeoid) thin, linear, small, narrow, pale green and are arranged in whorls of 3- 4. They lack any stomata and are without palisade parenchyma.

Jussiaea

Is a submerged - floating hydrophyte. It is found in shallow ponds. It is rooted to the soil. It has a slant , delicate stem with nodes and internodes but without leaves. The emergent portion of the stem possess normal leaves. The submerged stem produces certain whick like cottony roots from their nodes, often in clusters. They arerect facing upwards, submerged within the water, sometimes emerging out slightly. They are called respiratory roots. They are helpful in respiration and buoyancy as well. The normal roots are cut out as usual from the nodal regions growing down wards. Since there are no leaves in the submerged portions, the plant doesn't provide any resistant to the flow of water. The plant body is spongy, hence helpful in buoyancy.

Pistia: (Araceae)

Pistia is a free floating form; found in fresh water ponds. It grows of means of offsets. The leaves arise in a rosette at a node. They are round, or spathulate. A cluster of adventitious roots arise from a node below the rosette of leaves. They bear root pockets (not root cap). The stem is spongy and grows horizontally on the rosette spread horizontally on the surface of water. The outer leaves of the rosette spread horizontally while the inner leaves remain erect. This arrangement keeps the plant floating on the surface of water. The leaves being aerial, possess cuticle, stomata and palisade parenchyma. The stem is spongy due to the air spaces in the cortex. Mechanical tissue is absent - thus exhibiting typical hydrophytic features.

Eichhornia (Pontederiaceae)

It is a free floating hydrophyte. The stem is horizontal, an offset and is spongy. The leaves arise in a cluster at the node. They are large, thick fleshy with inflated petiole and an expanded lamina.

The surface of the leaves is covered over by water - proof cuticle. Air is stored in the spongy petiole. That makes the plant buoyant. The roots are adventitious and bear root pockets. They act as balancers.

Nympheae

It is a rooted and floating hydrophyte. The plant is rooted to the soil at the bottom of the shallow pond. The stem is stoloniferous, creeping along the surface of the soil at the bottom. The long petioles emerge out from the nodes towards the surface. The lamina is exposed on the surface of the water level. The entire body is spongy and hence helpful in buoyancy.

Limophila

It a rooted emergent hydrophyte. The stem is delicate. The submerged portions of the stem possess dissected leaves at their nodes. They look like roots, but they are green. The emergent leaves are normal. The dissected leaves do not provide any resistant to the water flow of the pond. Since the plant shows two types of leaves a) normal leaves.

Dissected leaves, the condition is termed Heterophylly
.

T. S of Hydrilla stem

Hydrilla exhibits typical hydrophytic features -

1.     Epidermis without cuticle.

2.      Aerenchymatous cortex. The air spaces are separated by single layered partitions.[one

or two layers of cortex just below the epidermis and outer to the endodermis are

without any air spaces but possess intercellular spaces]

3.     The endodermis and peri cycle are indistinct.

4.     Mechanical tissue is absent.

S.     Only a few xylem elements are present towards the centre or it may be replaced by a

cavity in the centre.

6.Phloem is well developed
. 
T.S of Jussiaea stem

T.S of stem shows the following structures:

1.     Epidermis, without cuticle.

2.      Cortex differentiated into 3 - regions  the outermost hypodermis, middle

aerenchymatous zone with large intercellular air cavities separated by thin diaphragms and the innermost region surrounding the stele with compact

parenchyma.

3.     Endodermis - of thin walled cells.

4.      Vascular bundles _ conjoint, collateral and are arranged in a ring. Phloem and xylem

are poorly developed. The xylem tissue does not show typical thickenings.

5.     Pith - well developed with loose parenchyma.

T.S of Nymphaea petiole

T.s.of Petiole shows the following features:

1.     Epidemis without cuticle.

2.     Stomata absent.

3.     Cortex elaborate with abundant aerenchymatous spaces.

4.     Vascular bundle are enclosed within the stele.

5.     It has certain aerenchymatous gaps.

6.     Vascular bundles are represented by one or two metaxylem points & 2 - 3 protoxylem

points.

7.      Raphides or druses may also be present in the cortex, which are protective in function
.

MESOPHYTES

T.S OF YOUNG DICOT STEM

1.     Upper and lower epidermis: Both are composed of a single layer of cells covered by cuticle. Both bear numerous multicellular hairs or trichomes. The epidermal cells do not contain chloroplasts. The lower epidermis has numerous stomata, each with a pair of guard cells, opening into a large respiratory cavity.

2.     Mesophyll: It is the groung tissue of the leaf divisible into an upper palisade parenchyma and a lower spongy parenchyma. The former consists of elonhgated cells, closely packed with very narrow intercellular spaces. The latter consists of spherical or irregular cells, loosely arranged, and with numerous large intercellular spaces.

3.     Vascular bundles: These are represented by the midrib and the veins. Each is conjoint, collateral and closed. Each has a bundle sheath of parenchyma. Xylem lies towards the lower. In the midrib region, just inner to the epidermis, there is collenchyma tissue, forming bundle sheath extensions. There may be a few patches of sclerenchyma associated with xylem and phloem.

XEROPHYTES

Asparagus (Liliaceae)

A drought enduring non succulent xerophyte- with leaf like axillary branches called cladode. It has only one internode. Cladodes are cylindrical, green, and photosynthetic. The leaves are reduced to prickles. The roots are fasciculated and they store food which will be utilized during the drought.

The cladode of Asparaus has some special structure, specially adapted for xerophytic habit - outer most epidermis with thick cuticle, some stomata distributed here and there. 

It is followed by a palisade like layer having elongated cells with chloroplasts. Below it is the spongy tissue of a few layers. In the centre is present a single vascular bundle. surrounded by a few layers of parenchyma and a layer of sclerenchyma.

Ruscus (Liliaceae)

This is a small xerophytic shrub. The branches are leaf +Iike organs, green, flat arising in the axils of a scale - leaf and are called cladodes, The cladode must possess single internode. But the cladodes here, bear male or female flowers (Ruscus is dioecious) from a point (representing a node) half way upon their surface in the axil of another scale- leaf. Therefore some authors consider the modified organ as the phylloclade.

Ruscus shows xerophytic adaptations, in its anatomical construction. A thick cuticle over the epidermis, followed by compact chlorenchyma with a few intercellular spaces well developed amphivasal (phloem surrounding the xylem) scattered vascular bundle surrounded by sclerenchyma are some such features.

Opuntia (Cactaceae)

It is a wild spiny shrub of arid places. The flattened green stem segments called phylloclades are thick and fleshy (succulent) and carry out the function of photosynthesis. The phylloclades contain a lot of mucilage which helps in retaining water for a long time. Each phylloclade bears several areoles (nodes). Each areole has one or more spines representing the axillary branches and a number of bristles which are modified leaves of axillary branches. The leaves are thus completely absent. The spines and bristles protect against grazing animals and also cut down transpirarion.

Euphorbia tirukalli ( Euphorbiaceae)

A succulent Xerophyte. The stem, green, cylindrical modified into a phylloclade and succulent. It performs the function of photosynthesis. It also functions as a storage tissue, retaining plenty of water. Abundant latex is present. Leaves are very much reduced. Root system is very extensive.

Anatomically, it shows the following xerophytic adaptations _ thick cuticle, sunken stomata, cortex with very little intercellular spaces, chloroplastids distributed in the well -developed 'palisade' distributed in thee cortical region) and well developed vascular system. All these xeromorphic adaptations adaptations.help the plant in checking the transpiration rate resisting the drought conditions.

Casurina

The phylloclade is provided with alternate ridges and furrows. Stomata and a few multicellular hairs are present in the furrows. Epidermis has its outer wall thick and has thick cuticle. Hypodermis is present beneath the ridges in T _ shape, composed of sclerenchyma. It is followed by a few layers of palisade chlorenchyma cells. Cortex is parenchymatous, also present beneath the furrows. Well developed vascular bundles are in two rings. In the middle of which is the endodermis. The outer cortical bundles are located below the ridges within the cortex, and the normal bundles lying below the endodermis are located opposite to furrows. Secondary growth takes place in the stem only in the inner ring of bundles. PericycIe is scIerenchymatous nature are present above to all the vascular bundles , pith and medullary rays are well represented. The unique construction of the stem is a xerophytic adaptation.

Phyllode in Australian Acacia (Acacia auriculiformis): 

Phyllode is a flattened petiole and the primary rachis, resembling the lamina in its shape. It is sickle shaped. It is thick & tough, flattened or winged leaf like, non - succulent and photosynthetic in function. The leaf is bipinnately compound in the young seedling stage. The leaflets and secondary rachii are shed and only the primary rachis grows into phyllode. The phyllody reduces the transpiring surface. This is a xerophytic adaptation.

The xerophytic adaptations are well represented even in its anatomical construction - well developed cuticle over the single layered epidemis, sunken stomata, well developed palisade and parenchyma with very little intercellular spaces, well developed vascular bundles, which are conjoint, collateral, and arranged in a ring below the palisade surrounded by sclernchyma - are some of the xerophytic features.

Aloe (Liliaceae)

Aloe is a leaf succulent xerophyte. It is a drought resisting plant, avoiding drought by means of water reserves. Succulence is due to the proliferation of parenchymatous cell accompanied by an enlargement of vacuoles of mature cells and a considerable reduction in the size of intrcellular spaces. The succulents shrivel during the periods of drought as they become depleted of water; but this shrinkage doesn't result in any damage to the plant. A thick cuticle, sunken stomata, lesser intercellular characters. Since succulents avoid drought by means of water reserves, some exclude them from the category of true xerophytes. However, Daubenmire feels that they are unique in their mode of adaptation among xerophytes and they are best represented in desert vegetation.

HALOPHYTES

Spinifex

It is a psammophyte. It is a sand binder, growing along the sea cost upon the sand. It has a running stoloniferous stem . which branches profusely on all directions. The leaves are sheathing, tough with sharp margin & spiny tip. The pockets formed at the nodedue to the sheathing leaf bases store water and keep the plant moist and cool

The inflorescence, the cluster of spikelet develop into infructescence after fertilization. The stylar part of the gynoecium develop into sharp bristled awns. Each spikelet grows into an achene. All achenes are found clustered along with the sharp pointed awns in the form of a ball. It is light weighted. It can be carried very easily in the sea cost along with the wind current, thus helping in fruit dispersal.

Salicornia

Is a succulent xerophytes, found along the sea cost as a sand binder. It has a jointed stem, with brown scale leaves arising from the nodes protecting the internodal part. The roots arise from the nodes. The branched stem is a phylloclade, protecting the sand from sand erOSIOn.

Vivipary in Rhizophora:

Rhizophora is a typical halophyte, usually forming the 'formation' in the mangroves. The development and growth of embryo (germination) in the seed when the fruit is still 

attached to the plant - is termed vivipary. This adaptation is a precaution against the failure of germination of seeds in saline soils, which are deficient in oxygen. In Rhizophora, the embryo grows out into a small 'seedling' with green hypocotyl (which can photosynthesize) and radicle discarding the seed coat and the fruit wall. The "seedling" gets detached from the mother plant, fall vertically down on the muddy saline soil, as a result the radicle gets embedded in the soil. Further, the viviparous embryos have a leathery texture, enabling them to float, if fallen on water.

Stilt root of Rhizhophora:

Halophytes which occupy the foeward line of the shore facing the sea (or the wind) are in the form of a small tree fixed to the muddy soil by special adventitious fixing roots - stilt roots. Rhizophora is one such example. The stilt roots one such example. The stilt roots provide additional support for the plant to face the wind. Further, these roots are also provided with lenticels, which enable them in aerating the internal tissues of the plant. The deficiency of air in the muddy soil is thus compensated by the development of lenticels, on the stilt roots.

Pneumatophore of Avicennia (Verbenaceae):

Avicennia is a marshy halophyte commonly found in a mangrove, spreading roots into shallow water. The saline soil frequently become water logged and to counteract, this lack of aeration of the root zone. Avicennia root branches which grow erect until they project above the poorly aerated muddy soil surface. These are pneumatophores. These are otherwise called breathing roots. They are provided with air pores or lenticels, thin cork, highly developed intercellular spaces; thus enabling free movement of air inside.

T.S of pneumatophore of Avicennia:

The anatomical structure of pneumatophore resembles that of a stem in the nature and disposition of the vascular systems in particular. A transverse section show the following arrangement of tissues:

1.     Cork - a few layers thick with smalllenticels, for the absorption of oxygen.

2.     Cortex - massive, parenchymatous with well developed intercellular spaces - air

chambers.

3.     Endodermis - uniseriate and peri cycle made of parenchyma and sclerenchyma.

4.     Stele - collateral and open.

S. Pith - is parenchymatous in the centre
.

EPIPHYTES

Vanda (Orchidaceae):

Vanda is an epiphytic orchid. Epiphytes are plants which grow upon other plants but do not derive nutrients and water from the supporting host, and have no connection with the soil.

Vanda is a proto epiphyte (Schimper's classification) as it finds its nutrition in the rough bark of the host. The plant produces clinging roots for fixation and they form net like structures at the base to collect water and humus. Velamen roots are those which hang

freely in the air and has velanen tissue inside and they are hygroscopic. Stem is reduced. Leaves are succulent, with thick cuticle (xerophytic features) and they practice water economy.

Bulbo'phyllum: (Orchidaceae)

 It is an epiphyte as it dwells in the rough bark of host trees. The plant body consists of an horizontal rhizome with swollen succulent pseudo bulb at each node. These pseudo bulbs are modified branchlets of one internode. They observe water economy  by storing water in these pseudobulbs. The epiphyte attaches to the host only through the clinging roots.

Delldrobium

It is a protoepiphyte growing on the tree barks with the help of perching roots. It has no aerial roots or velamen roots. The stem is a phylloclade, erect, jointed, with greyish scale leaves protecting the internode. The normal leaves are seen only during the rainy season. During flowering season leaves are not seen. It reduces transpiration. The stem is succulent and can store water for prolonged period of time. Since there are no special adaptations as such for epiphytic mode of life, dendrobium is classified under proto epiphytes.

Drynaria (Polypodiaceae - Fern)

It is a nest epiphyte - a fern. It produces two kinds of leaves

1.     Pocket leaves attached to the rhizome to form a nest.

2.     Normal pinnatified frond.

Short roots produced from the rhizome enter into the 'nest' for absorbing water and debris. Here attaching roots are absent - rhizome itself attaches to the host tree by some gum like secretion.

T. S. of velamen root of Vanda:

The velamen root is a special kind of aerial root produced by an epiphyte. It is a freely hanging greenish spongy root, of hygroscopic nature. It also carries out a little carbon assimilation, because of the presence of chlorophyll.

The velamen tissue is the outer spongy tissue, which is many layered - compactly set non living cells. It represents a multi seriate epidermis. They have their walls variously thickened, by spirally or reticulately arranged fibres.

The outer most layer of cortex is the exodermis having suberin thickenings over the outer and lateral walls unthickened ones, called passage cells, occur here and there, which may serve as channels for the flow of water absorbed by the val amen. Cortical cells have chloroplasts and they are photosynthetic in function. Endodermis has also some passage cells against the proto xylem vessels. Mechanical tissue is present (sclerenchymatous) intermingled with the well developed vascular bundle. Central portion is the parenchymatous pith which usually undergoes sclerosis.

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