rooted hydrophyteswith floating...

By,Ms. RojaLecturerDept. of Botany

CHARACTERS HYDROPHYTES XEROPHYTES HALOPHYTESMorphological adaptation:

1).Root: • Poorly developed, reduced or absent• Not required for the absorption of

water or nutrients.• The entire plant surface can absorb

water and minerals.• Root caps usually absent.• root pockets or root sheath present.

• Floating roots are negatively geotropic and they are spongy in structure.

• Spongy roots help the plant to float in the water.

Ex: Jussiaea repens

• Well developed in true xerophytes.

• They are adapted to reach the area where water is available and to absorb water as much as possible.

• Profusely branched and more elaborate than their stem.

• Most of the roots in xerophytes are perennial and they survive for many years.

• Roots grow deep into the soil and they can reach a very high depth in the soil.

• Root surface is provided with dense root hairs for water and mineral absorption.

• Develop many shallow normal roots.

• In halophytes, in addition to normal roots, many stilt or prop roots develop from the aerial branches of stem for efficient anchorage in muddy or loose sandy soil. e.g., Rhizophora mucronata, the stilt roots may be strong and extensively developed, but in others they may be poorly developed (Rhizophora conjugata).

• Halophytes develop special type of negatively geotropic roots, called pneumatophores or breathing roots .

Jussiaea repens showing spongy respiratory roots.

Rooted hydrophytes with floating leaves.

free floating hydrophytes

Pneumatophores of mangrove plant

Supporting or stilt roots of mangrove plantsdeveloping from the trunk Ulex Stem

2)Stem • Delicate and usually green in colour.• Modified into rhizome or runner.

• Stem woody and hard in few.• Usually green and photosynthetic.• Covered with thick cuticle, wax and silica

(Example: Equisetum).• In many plants, the stem is covered with

dense hairs (Example: Calotropis).• Stem modified into thorns in Ulex.• Succulent and bulbous xerophytes can

store water in their stem. Example: Cactus and some species of Euphorbia.

• Stem may be modified into phylloclade, cladophylls or cladodes.

• Phylloclade: Stem modified into flattened leaf-like organs(Muehlenbeckia).

• Cladode: Many axillary branches become modified into small needle like green structures which look exactly like leaves(Asparagus).

• Cladophyll: branches developed in the axil of scale leaves, become metamorphosed to leaf-like structures (Ruscus).

• Stems in several halophytes develop succulence. Salicornia herbacia and Suaeda maritimamay be quoted as familiar examples for it.

• succulence depends on the ratio of absorbed to free ions in the plant cells rather than absolute amounts of sodium chloride or sulphate present.

Rooted submerged hydrophytes

A, B & C – Phylloclade and cladodes. A –Phylloclade of Cocoloba. B – Cladodes of Ruscus. C – Cladodes of Asparagus

Morphological adaptation

Hydrophytes Xerophytes Halophytes

3)Leaves: • In floating hydrophytes, the leaves are long, circular, green, thin and smooth.

• In these plants, the upper surface of the leaf is exposed to air whereas the lower surface touches the water.

• In Lotus, the petiole show indefinite growth and thus always keeps the leaves floating in the water.

• Heterophylly (morphologically different leaves in a single plant) is present in some plants.

• Leaves usually absent in xerophytes.

• If leaves are present, usually they are caducous (fall off easily).

• Most of the cases the leaves are modified into spines or scales(Casuarina).

• Leaf may modify into phyllode in some plants.

• Phyllode: leaf petiole or rachis modified (flattened) into leaf like organ Example: Acacia.

• The leaves in most of the halophytes are thick, entire, succulent, generally small-sized, and are often glassy in appearance.

• Some species are aphyllous.

• Stems and leaves of coastal aero halophytes show additional mode of adaptation to their habitats.

• Their surfaces are densely covered with trichomes. Leaves of submerged marine halophytes are thin and have very poorly developed vascular system and frequently green epidermis. They are adapted to absorb water and nutrients from the medium directly.

Rooted emergent hydrophytes with heterophyllyCasuarina

Succulents Development of phyllode

Morphological adaptations:


• In heterophyllous forms, the submerged leaves are linear or ribbon like or highly dissected, whereas the floating leaves or aerial leaves are usual or circular shaped.

• The leaves of free floating hydrophytes are with smooth waxy surface.

• The wax coating protects the leaves from chemical and physical injuries.

• They also prevent water clogging of stomata during rainy seasons

• In Eichhornia, the leaves are with swollen and spongy petiole for providing buoyancy.

•The root system is very well developed with root hairs and root caps. e.g. Calotropis.•The roots are fasciculated as in Asparagus.• Stems are stunted, woody, dry, hard, ridged, and covered with thick bark, may be underground, e.g. Saccharum. In Opuntiaphylloclade is covered with spines.• Stem is covered with thick coating of wax and silica in Equisetum or dense hairs as in Calotropis.•Stems may be modified into a thorn e.g. Ulex or cladodes e.g. Asparagus.• Leaves are very much reduced, small scale-like, appearing only for a brief period (Caducous) sometimes modified into spines or scales as in Casuarina, Ruscus, Asparagus.• Lamina may be narrow or needle like as in Pinus or divided into many leaflets as in Acacia or succulents as in Aloe.

• Viviparous mode of seed germination:

• Halophytes or mangrove plants growing in the tidal marshes are met with the phenomenon of ‘vivipary’ which is defined as the germination of seeds while the fruits are still attached to mother plants

• The fruits and seeds are generally light in weight. Fruit walls have a number of air chambers and the fruits, seeds, and seedlings which can float on the water surface for pretty long time are dispersed to distant places by water current.

Vivipary in Rhizophora

Salicornia herbacea a succulenthalophyte

Mangrove forests (Sunderbans)

Inflorescence of Spinifex squarrosus

Anatomical adaptations:


(a). Reduction in protecting structures:• The cuticle is totally absent in

submerged parts of hydrophytes.• In aerial parts, the cuticle may present

as a very thin layer.• Epidermis is NOT the protecting layer.• Epidermal cells contain chloroplasts.• Epidermal cells can absorb water and

nutrients.• Hypodermis poorly developed, cells are

thin walled.

(a). Roots:• Root hairs are well developed in

xerophytes.• Roots with well-developed root

cap.• In Asparagus, the roots become

fleshy and store plenty of water.• In Calotropis, root cells are with

very rigid cell wall.

• Anatomy of halophytes reveals a number of xerophytic features in them. These are as follows:

• (I). The stilt roots of mangrove plants show normal features with periderm on the surface, aerenchymatous cortex containing sclereids, normal endodermis, secretory pericycle, radially arranged xylem and phloem and extensively developed pith.

• Pneumatophores develop a number of lenticels on their surface.

(b). Increase in the aeration:• Stomata is completely absent in

submerged parts of hydrophytes.• Exchange of gases in hydrophytes takes

place through the cell wall.• In floating plants stomata confined to

upper epidermis of the leaf.• The aerenchyma is well developed in

submerged plants.• Air chambers in the aerenchyma are

filed with respiratory gases and moisture.

(b). Stem:• Epidermis is well developed

and with thick walled compactly packed cells.

• Cuticle is very thick and well developed over the epidermis.

• Hypodermis is several layered; often hypodermis will be sclerenchymatous(Casuarina).

• Stomata are present on the stem for gaseous exchange and transpiration.

• Presence of thick cuticle on the aerial parts of the plant body. The epidermis of xerosucculentsand coastal halophytes is characterised by a cover of waxy layers in addition to thick cuticle.

A,B-T.S of submerged leaves, A-vallisneria and B-ceratophyllum

T.S of Hydrilla stem

V.S of an amphibious leaf

Anatomical features of some hydrophytic leaves

T.S of Nerium leaf lamina showing multilayered epidermis, compact mesophyll and hairy stomatal pit

Anatomical adaptations


• (c). Reduction of supporting or mechanical tissues

• Mechanical tissues are absent or poorly developed in hydrophytes.

• Thick walled sclerenchymatous cells totally absent in hydrophytes In Nymphaea, special type of star shaped lignified cells (asterosclereids) present which will provide mechanical support.

• Main function of roots is to anchor in the soil (NOT the absorption of nutrients and water).

• Stomata are present on the stem for gaseous exchange and transpiration.

• Stomata are sunken type and usually situated in pits provided with hairs (Casuarina).

• Vascular tissue is well developed with prominent xylem and phloem components.

• In most of the xerophytes, the bark will be well developed and thick.

• Many oil and resin canals are present in bark.

• Most of the cases, the stem will be photosynthetic and contains chlorenchymatous cells in the outer cortex.

• In the stem of Casuarina, the chlorenchymatous cells are radially elongated and palisade like tissue in appearance.

• Stems in the succulent plants possess thin-walled water storing parenchyma cells in them. Mucilage cells may be found in abundance. Epidermal cells of various mangrove species contain large quantities of tannins and oil droplets. Cortex is fleshy, several cells thick and in old stems it may become lacunar. Salinity causes extensive lignification of stele

• (d). Reduction in the vascular tissues• Vascular elements are poorly developed

in hydrophytes.• Absorption of water and minerals takes

place through the cell surface.• Thus very little importance is there for

vascular tissues.• The xylem is highly reduced in the

vascular bundles of hydrophytes.

(c). Leaf:• Epidermis of the leaf is thick

and may be multilayered.• Thick cuticle present over the

outer tangential wall of the epidermal cells.

• In some plants, the epidermal cells can store water.

• Leaves may be dorsiventral or isobilateral. They develop protected stomata which are not deeply sunken. Epidermal cells are thin-walled. The palisade consists of several layers of narrow cells with intercalated tannin and oil cells.

T.S of Marsilea rhizomeAnatomy of leaf of typha

Rhizphora mucronata - Transverse section ofyoung stem

Rhizophora mucronata - V.S of leaf showing detailed structure

Anatomical adaptations Hydrophytes Xerophytes Halophytes• Usually, the xylem is represented

by few tracheids only.• Sometimes the xylem not at all

developed.• hloem usually ill developed,

sometimes well developed.• Vascular bundles are arranged

towards the centre of the organ.• Secondary growth totally absent.

• These cells are called bulliformcells.

• Bulliform cells are motor cells and they assist in leaf rolling to reduce transpiration.

• Hypodermis usually present.• In Pinus, the hypodermis

sclerenchymatous.• Mesophyll is well developed in

xerophytic leaves.• Many layered palisade tissue

present.• Spongy tissue is less developed in

xerophytes with less intercellular spaces.

• Leaves of Aloe have water storing region in the mesophyll.

• Stomata are reduced in numbers and are situated only on the lower sides of the leaves (hypostomatic leaves).

• Stomata are sunken type and usually situated in pits with hairs (Nerium).

• Vascular tissue is well developed with plenty of xylem elements.

• Mechanical tissue well developed in the leaves of xerophytes.

• Transfusion tissue, if present, will be well developed for the lateral conduction.

• The leaves and stems of coastal halophytes are abundantly covered with various types of simple and branched trichomesgiving the plants a greyish appearance .

• The trichomes may exert a protective function in plants by:

• (a) Affecting water economy,• (b) Affecting the temperature of

the leaves, and• (c) Preventing sea water droplets

from reaching the live tissues of leaves

• Leaves of many species of mangrove are dotted with local cork formation “cork warts”.

• Leaves of Sonneratia and Aegiceras and Nitraria (a desert shrub), Suaeda monoica contain well developed aqueous tissue

• Salt secreting glands may be found in some halophytes.

Physiological adaptations:


• Low osmotic concentration of cell sap in hydrophytes.

• The osmotic concentration is equal or slightly higher to that of surrounding water.

• This prevents the unnecessary entry of water into the cells.

• Water is absorbed by the entire plant surface.

• Nutrients are absorbed by entire plant surface.

• Gaseous exchange takes place through the entire plant surface.

• Both stem and leaves can do photosynthesis.

• Oxygen produced by photosynthesis is retained in the air cavities.

• Structural or morphological adaptations of xerophytes are well suited to survive in drought conditions.

• Xerophytic plants are reported to contain pentosan polysaccharides which are reported to offer resistance against drought conditions.

• Many xerophytes show CAM (Crassulacean Acid Metabolism) cycle.

• In CAM plants, the stomata will be closed at day time.

• Stomata open during the night and they absorb enough carbon dioxide for the photosynthesis.

• Absorbed carbon dioxide is converted into malic acid and store in the vacuoles of the cells.

• The malic acid increases the osmotic concentration of cell sap and this enables the closure of stomata in the day time.

• They show high rates of transpiration,

• They show exudation of sap that contains dissolved salts,

• They develop many shallow absorbing roots.

• Saline conditions are not essentially “dry” for all plant species. Under saline conditions sometimes higher transpiration rates have been observed in halophytes than in neighbouring salt hating plants

• It should, therefore, halophytes show xeromorphism for enduring high salinity of soil water and also for absorbing water with perfect ease.

• . It seems reasonable because of the fact that sodium salts if present in the soil water will definitely stimulate succulence even in non-halophytes and characteristic succulence of some plants may disappear if they are grown on the soil lacking in these common salts.

Physiological adaptation:


• This oxygen is utilized when required.

• Transpiration absent in submerged plants.

• Emerged plants and floating plants have excessive transpiration.

• Mucilage cells produce plenty of mucilage.

• Mucilage prevents the decay of plants in the water.

• Vegetative reproduction is the most common method of reproduction

• Pollination and dispersal of fruits in hydrophytes are facilitated by water

• Some enzymes such as catalase and peroxidase are more active in xerophytes.

• Amylase enzyme in xerophytes is more efficient in the hydrolysis of starch than mesophytes.

• Xerophytes can regulate the rate of transpiration.

• They ensure the reduced rate of transpirational loss of water by thick cuticle, distribution of stomata in the lower side of the leaf, sunken type of stomata, and positioning of stomata in pits with many hairs.

• Xerophytes possess high osmotic concentration of cell sap.

• Thus cells have high osmotic pressure.

• High osmotic pressure increases the turgidity of the cells.

• Turgidity exerts tension force (turgor pressure) on cell wall.

• Excessive accumulation of sodium does not harm these plants. Halophytes grow in saline habitats not because they are salt loving but because they tolerate high concentration of salts better than other plants of non- saline habitat.

• Active accumulation of salts also increases the osmotic concentration of cell sap in these plants and thus makes them able to absorb salty water very easily.

Succession of Mangrove Vegetation in Sea Coast:• The distribution of a halophytic

community appears to be limited by salinity and depth of water table, as well as the competitive ability of the members of next community in the halosere (Reed, 1947). The aggressiveness of plant communities in saline habitat is due to changes in the salinity level.

Rhizophora mucronata T.S of a portion ofsubterranean stilt root

T.S of a pneumatophore

Physiological adaptation


• Due to this high turgor pressure, the wilting of cells is prevented by the extreme heat.

• High osmotic concentration also ensures the rapid and effective absorption of water.

• Tissue of succulents possesses mucilage to hold large amount of water.

• Loss of high proportion of body mass with rapid recovery when water is available.

• Produce brightly coloured, large and showy flowers for attracting pollination agents.

• Cactoid plants produce large amounts of minute seeds.

• Seeds are with thick seed coat for protection.

• Seed surface also possesses mucilage substances to absorb and hold water when it is available.

• Some plants quickly complete their life cycle before the unfavourable conditions.

• Efficient pollination mechanism by moths, bats and birds.

• In coastal region, nature of vegetation is greatly affected by the gradual elevation sea coast Succession of mangrove formation in coastal regions may take place very slowly in the following sequence:

• (1) In deep water generally true mangroves, e.g., the species of Avicenma grow.

• (2) When the bottom of the sea is slightly raised up, Avicennia, Rhizophora, Ceriops, Bruguieraetc. form mixed mangroves vegetation in the shallow water.

• (3) As the ground is exposed, true mangroves disappear and other halophytes, e.g., of Aegiceras, Icoecaria, etc. gradually invade the land within short period.

• Succession of angiospermichalophytes varies also in different habitats in accordance with other ecological conditions besides salinity.

Examples: Hydrophytes Xerophytes Halophytes• Examples are Utricularia.

Vallisneria, Hydrilla Chara NitellaLotus, Ceratophyllum, Trapa, Pistia, Eichhornia (water hyacinth), Wolffia, Lemna, etc .

• Examples are Opuntia, Echinocactus, Euphorbia royleana Aloe, Agave, Peperomia, Haworthia,Bryophyllum, Kalanchoe Nerium, Cassuarina, Pinus, Calotropis, Ephedra, Equisetum etc.

• Rhizophora mucronata, Kandeharheedii, Ceriops roxburghiana, Bruguiera gymnorhiza ,Avicenniaalba Avicennia marina, , Sonneratia. Acanthus ilicifolius, Myriostachya weightiana, Clerodendron inerme, etc.,

1)Nymphaea(water lily):External morphology:• It is a rooted aquatic perennial

Herb with floating leaves growing along shallow margins of ponds.the roots are adventitious and slender.

• The stem is root stock rooted in mud.

• The leaves are floating with long petioles(6-8 inches).lamina is heart shaped and keeps floating on the water surface.they are radical long 5-10 inches across.

• Flowers are white or pink and raised on a leaflets scape.

• The leaves have long cylindrical spongy and flexible petioles which have the power of renewed growth incase the water level rises. The lamina is peltate,cordate with slightly toothed margins.

1)OpuntiaMorphology:• Drought resistant succulent.• Extensive feeders root system.• Flattened green stem segment

called phylLoclades are thick fleshy and carry out function of PHOTOSYNTHESIS.

• Phylloclade store water and mucilage.

• Stomata are sunken and remain closed during day time.

• Xerophytic characters:• Shrubby habit.• Thick and fleshy phylloclade.• Spiny leaves.

1)Rhyzophora:Morphology:• These are the plants which

grows in saline marshy soil along the river mouth and are called physiological xerophytes.

• Root in mangrove plants is stilt roots and pnematophores.

• Leaves are thick fleshy and store water.

• Stem are thick and succulent.• Due to salinity they exhibit

viviparous mode of seed germination.

Examples Hydrophytes Xerophytes HalophytesHydrophytic features:• Adventitious roots with

arenchymatous middle cortex.• Floating Leaves with long

petioles.• Stomata on the dorsal surface of

leaves.• Air spaces in petiole and lamina

for storage of air.• Poorly developed xylem and

presence of mechanical tissue just below the epidermis in petiole and lamina

T.S of phyloclade of opuntia:Epidermis:• The surfaces are bounded on both

the sides by upper and lower epidermal layers. A thin cuticle covers the epidermis. The epidermis is interrupted by numerous stomata on both the surfaces. Distinct guard cells of the stomata and sub-stomatalchambers are visible.

Hypodermis: • Below the epidermis is 2-3 layered

collenchymatous hypodermis 3-4 layered palisade parenchymatoustissue is present the cells are filled with chlorophyll pigments.

Rhizophora mucronata:T.S. of Stem:1.Epidermis:• The stem has a very thick cuticle.

The epidermis is composed of variously shaped cells appearing conical in transverse sections. The epidermis frequently consists of more than one layer, but a true hypodermis of 3-7 layers is also common. The cork in young stems generally arises superficially, usually in the hypodermis. The young stem has a very thick cuticle.

Nymphaea-T.S of leaf:• A section through the leaf of

waterlily (Nymphaea stellata of family Nyphaeaceae) would reveal the following anatomical structure . As an aquatic plant it has extremely reduced vascular and supporting tissues and well-formed air chambers.

• The center of the stem is occupied by large thin walled cells which enclose a water and mucilage.

• Vascular bundles are enclosed in the storage parenchyma in the form of ring.

2.Cortex:• The primary cortex is lacunar. H-

shaped sclerenchymatousidioblasts are present. The cells of cortex possess pitted walls and are full of tannin and oil. Calcium oxalate crystals are also present. The inner cortex has groups of branched sclereids which give mechanical strength to the lacunate cortex.

Examples Hydrophytes Xerophytes Halophytes

I. Epidermis:• Epidermal layers are uniseriate

both on the adaxial and abaxialsides. They are composed of closely-set cells. Stomata occur on the upper side. Moreover, there is deposition of waxy matters which prevents wetting and clogging of the stomata.

II. Mesophyll:• It is differentiated into palisade

and spongy cells. A few layers of columnar cells occur towards the adaxial side forming the palisade. The spongy cells present towards lower epidermis and irregular in outline. Large air chambers are present in the mesophyll. Elongated sclerotic cells—the trichosclereids commonly called ‘internal hairs’, often with branched ends are frequently present.

III. Vascular Bundles:• These are very much reduced. As

usual they are composed of xylem and phloem, and remain surrounded by parenchymatousbundle sheath.

• The sclereids are lignified thick walled cells with narrow lumina. The endodermis is conspicuous. The endodermal cells possess starch grains.

pericycle:• It consists of a sub-continuous

composite ring of sclerenchymaconsisting of 3-4 layers of cells.

• Vascular Bundles:• The vascular bundles are conjoint,

collateral, endarch and open.Xylem:• The xylem is traversed by rays 2-3

cells wide in Rhizophora mucronata. The vessels possess scalariform perforation plates.

Crystals:• The crystals are generally

clustered.• Secretory Elements:• Vertically elongated secretory

cells containing tannin and/or oil present in the cortex and the pith.


Nymphaea-T.S of petiole(Waterlily):• The petiole of waterlily

(Nymphaea stellata of the family Nymphaeaceae) are characterised by large air chambers, branched trichosclerides or internal hairs with calcium oxalate deposition, and scattered vascular bundles with very poorly developed xylem elements.

• Transverse section of the petiole of waterlily shows the following anatomical features

(i) Epidermis:• The epidermis is made of a layer

of chloroplast containing roundish cells with little cuticularisation on their outer walls. Unbranched multicellularhairs are usually found on the epidermis.

• Anatomy of Leaf:• The leaves are usually

dorsiventral. Hairs are mostly unicellular with thick or thin walls. The cuticle is well-developed and often quite thick on both the leaf surfaces. Cork warts occur as small black spots on the lower side of the leaf. The epidermis is single layered and consists of rectangular cells.

• The cells of upper epidermis possess some rod-shaped and cubical crystals of calcium oxalate. The hypodermis towards the upper surface is 2 or more layered. The stomata are confined to the lower surface. They are depressed and often provided with a front cavity. The mesophyll consists of palisade and spongy tissue.

Examples Hydrophytes Xerophytes Halophytes(ii) Cortex:• The outer zone of the ground

cortex forms the 2-3 layered collenchymatous hypo-dermis with angular thickenings. Rest of the cortex is made of thin-walled parenchyma with large number of air chambers. Trichosclereids of peculiar shapes — often with deposition of cal-cium oxalate crystals — are abundantly present.

(iii) Vascular bundles:• Very poorly-developed vascular

bundles of different sizes remain scat-tered in the ground tissues. The xylem vessels usu-ally disintegrate and form lacunae which resemble the air chambers. The phloem elements are nor-mally developed. The smaller vascular bundles have a single patch of phloem, and compara-tively larger bundles have two patches of phloem.

• Palisade tissue consists of 1-4 layers. Spongy tissue usually possess large intercellular spaces. Aqueous tissue and mucilage cells are also present beneath the upper epidermis. H-shaped sclerenchymatous idioblasts occur in the palisade tissue, and variously branched ones in the spongy mesophyll

Anatomy of Breathing Root:• The well-known breathing roots

(pneumatophores) of members of the Rhizophoraceae inhabiting mangrove swamps have large intercellular spaces of the spongy cortex which facilitate gaseous exchange in the special habitat in which the plants grow. The cork consists of suberized cells.

• The cork layer remains interrupted by lenticels at several places. In some cases the cork consists of alternating layers of suberized and ordinary parenchymatous cells in the aerial portion. Next to the cork there lies a thick cortex containing abundant, large, intercellular spaces, arranged radially around the stele.

Rooted hydrophytes with floating leaves

Transverse section of a floating leaf of water-lilyNote larger air- chambers, mucilaginous glands and very much reduced vascular tissue.

Transverse section of petiole of Nymphaea (water lily)


2)Hydrilla: 2)Asparagus:

Morphology:• It is submerged anchored

hydrophytes found in ponds tanks and slow moving water.

• This plan is fixed to the substratum by adventitious roots with sparse root hairs.

• The stem is delicate,flexiblespongy and freely branched.

• The leaves are small thin sessile linear to lanceolate.

• They are in whorls of 3-8 at each node with unicostate ventation. leaves and stems lacks cuticle,stomata and mechanical tissues.

Morphology:• It is a non succulent xerophyte.• Plant body fasiculated root tubers

which store food and water.• Leaves are modified in to spins and

scales.• The stem is rigid and it contain

chlorenchymatous cortex and pericycle is sclerenchymatous.

• The cork layer remains interrupted by lenticels at several places. In some cases the cork consists of alternating layers of suberized and ordinary parenchymatous cells in the aerial portion. Next to the cork there lies a thick cortex containing abundant, large, intercellular spaces, arranged radially around the stele.

• Intercellular spaces are larger in the subterranean than in the aerial parts of the roots. The cortex may be subdivided into two portions-the secondary cortex and the primary cortex. The secondary cortex consisting of few layers is found just beneath the cork. The primary cortex lies next to secondary cortex. The primary cortex is broad and lacunar.

Hydrophytic characters:• Absence of root hairs.• Thinlinear,small,narrow,palegree

n leaves.• Herbaceous,thin, fistular stem.


Anatomy of hydrillastem:

T.S of cladode of asparagus:

ii) Stem:1. Stem is usually weak and flexible. Sometimes it is covered by a gelatinous sheath which serves as protection against periodic desiccation.2. The cuticle is either altogether absent or very poorly developed. The epidermis is always single-layered and thin-walled; this character facilitates direct absorption of gases and mineral salts dissolved in water.3. The cortex is very broad and occupies bulk of the stem. The outer layers of the cortex are parenchymatous and usually without inter-cellular air spaces, whereas the inner cortex is aerenchymatous and possesses symmetrically arranged large air spaces. The air filled in these cavities adds to the buoyancy of the plant and secondly facilitate the exchange of gases during respiration and photosynthesis.

• The outer most layer in this species has thick cuticle and stomata are distributed here and there.

• The stomata are followed by sub-stomatal cavities formed by palisade like layer having elongated cells with chloroplasts.

• They are green stems of limited growth (usually one internode long) which have taken over the function of photosynthesis from the leaves. The true leaves are reduced to scales or spines.

• The cladodes are leaf like in appearance with spiny tip, ovate outline and roughly parallel veins. The cladodes are borne in the axils of scale leaves. Moreover, a floral bud with a basal scale leaf develops in the middle of a cladode showing that the area represents a node.

• The primary cortex in the terrestrial part of the root is composed of cells of two kinds:

• (a) Radially elongated cells connected with one another tangentially by short lateral arms;

• (b) Rows of vertically elongate cellswhich show small, circular lumina in transverse sections. Solereder has recorded the ridges of thickening which are supposed to give mechanical support to the radially elongated cells where they are found.

• However, according to Bowman these are really cells filled up with mucilaginous sap. Mullan (1933) states that the cortex in the aerial part of the root system of Rhizophora mucronata Lam. is much reduced and the lacunae small. Sclerenchymatousidioblasts also occur in the cortex.

Phylloclade of Opuntia (Chhitar Thor)Cladodes of Asparagus

Examples Hydrophytes Xerophytes Halophytes• 4. The cells of the cortex contain

chloroplasts and assist in carbon assimilation.

• 5. Usually there is no marked distinction of endodermis and pericycle. Sometimes the inner-most layer of the cortex is regarded as endodermis. 6.Vascular tissue is poorly developed and does not show marked differentiation of phloem and xylem. An air cavity is mostly present in the centre of the vascular strand that adds to the buoyancy of the plant. Sometimes, xylem is represented by a single strand present in the centre of the stele (e.g., Hydrilla, Potamogeton, Elodea etc.)

• 7. There is no mechanical tissue present in the stem of the submerged plant. Water column itself provides mechanical support to the plant.

• The cladodes are slightly flattened, fleshy, and straight or curved pointed structures which develop in clusters in the axils of scale leaves. Each cluster represents a Suppressed cymosely divided branch with a few smaller scale leaves bearing cladodes in their axils. The main stem possesses leaf spines. Like phylloclade’s, cladodes are a modification to reduce transpiration.

• H-shaped sclerenchymatousidioblasts project into the cortical intercellular spaces in the aerial part of the root, but are less numerous below ground. Mullan(1933) has also recorded the vertically elongated tubular cells, filled with tannin and oil, situated at the junctions between the branched cells in the terrestrial part or the root of Rhizophora mucronata.

• The endodermis is conspicuous. Numerous secretory cells are found in the peri-cyclic region. The xylem is well formed and strongly lignified. The outer pith is sclerenchymatous whereas the central region of pith is parenchymatous. Several oil cells are present here and there in the pith region.


2)Avecenia T.S of leaf:• Avecenia is halophytes.• Leafs of T.S show upper

epidermis and lower epidermis.upper epidermis is cutinized while lower epidermis is interrupted by the presence of sunken stomata

• Lower epidermis also shows the presence of hair(peltate).

• Upper epidermis followed by few layers of water storage tissue.

• Mesophyll is differentiated into palisade and spongy tissue.

• Below the storage tissue palisade tissue is present.

• Close to the lower epidermis spongy tissue is present.

Thank you…

rooted hydrophyteswith floating...

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