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Water Regimes and Ecological Adaptat ·, , --- --- --- --- --- --- ---- -'On,, --- --- --- --- ---thesis, per unit, 62, , Water Regimes and Ecological Adaptations, , 63, , of transpiration as well as photosyn, area, higher osmotic pressure with an increase in, protoplasmic permeability and decrease in its, viscosity, grater resistance to wilting, and early, nowering and fruiting., , ECOLOGICAL GROUPS OF, PLANTS, The ecological groups of plants are indeed much, broader groups without any airtight boundari es, between them. This is a classification or rather a, very broad grouping of plants based on their water, relationships. E. Warming (1909) classified plant, communities on the basis of plants' depende nce, upon and relation to water, as done earlier by, Water as an, Grabner (1898, 1901 , 1908)., position, foremost, the, occupied, factor, ecological, , me., , E. Warming, , in distribution of vegetatio n and its structure, On the basis of their water requircmcni1., Warming primarily recognised three major grou p;, of plants:, I. Aquatic plants (hydrop hytes). They grow, in abundance of water with their lower parts i.e.,, roots, rhizomes etc., and leaves immersed in water., , fronds, , ~, , =water- =-=--- --:. ., Wolfffa, , frond, ody), , frond, , usots _, , - - · - - ---, , ot et, Sp/rode/la, , Eichhorn/a, , Lemna, , _, , Trapa, , merged, , ►•, , , , . OOts, , IAAV8S), , Nelumbo, , 2. Land or ter restrial pla nts. They grow in, normal water conditions with their assimilatory, orgi:m~ adapted to existence in air. Land plants, exhibit many grades of adaptation to their mode of, life. Thus, those which encounter greatest difficulties, in securing water are the xerophytes, while others, :15 mesophytes, which in some respects occupy an, mtermediate position between the two extremes, the, hydrophytes and the xerophytes., . 3. ":elophytes or marshy plants. They are an, mtermediate group between acquatic and land plants., An account of these ecological groups of, hydrophytes, mesophytes, xerophytes, ·, plant, an s, i.e.,, d halophytes will be presented here., , leaves, , wale, _, , ct ::.. ~, stem _, , --, , -, , Sa/vln/a, , Azol/a, , I, , Yig. 4.2. Free-floating hydrophytes. ,, , - root, Plstia, , Le_aves in some are very minute, while in others, qutte large. Some of the free-floating hydrophyt es,, as Wolffia, lemna, Spirodella, Azolla, Eichhomia, Salvinia and Pistia are shown in Figure 4.2. ·, , 2. Rooted Hydrophytes, with Floating Leaves, Their roots are fixed in mud, but leaves have, long petioles which keep them floating on the, water surface. The remaining plant, except leaves., remains in water. Some of the rooted hydropbytes, with floating leaves, as Trapa, Ne/11111bo,, Nymphaea and Marsilea are shown in Figure 4.3., , 3. Submerged Floating Hydrophytes, , HYDROPHYTES, , -, , Mars/lea, , Fig. 4.3. Rooted hydropb~ with floating leaves,, , floating, leaves, , water, su merg sporoca rps_ leaves _ __, , Nymphaea, , They grow o n extremely wet soil where water is, avai) b, th a le. to plants in abundance. According to, r,.~.way m Which they develop in water, they are, '"'UJer . subdi VI'ded into the foUowing five, categ, ones:, , 1. Free-Floating Hydrophytes, They rem . ., not soi) am m contact with water and air, but, · They float freely on the water surface., , They remain in contact with only water, being, completely submerged and not rooted in the mud., Their sterns are long and leaves generally small., Some of the examples are Ceralophy/111111,, Utricularia, Najas, etc. In Ceratophy/lum, (Fig. 4.4),, roots are lacking even in embryo stage, sometimes, leafy branches being modified into 'rhizoids'., , 4. Rooted Submerged Hydrophytes, These are hydrophytes Like Hydrilla, Potamogeton,, lsoetes and Valli.meria (Fig. 4.5) that remain, completely submerged in water and rooted in soil., (BC-4)

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rvc:::uc, ,, , IC~II' n,,...,, , u, IU t..vv,vy,c.,·a, Adapt ., , J~ -~66~--------------;;::__:_:_:_:_:;:~~x;~~~;~~:;::;~-:~_:_:_:_:_:_:_:_:.:::at,onsI, , Adaptations, water Regimes and Ecological, , 67, , Leaves, (1) In submerged forms, leaves are thin. and •~, either long and ribbon-shaped as m, Vallisneria (Fig. 4.5), or long and linear as, in Potamogeton (Fig. 4.5), or finely dissected, as in Ceratophyllum (Fig. 4.4). Floating, leaves are large, flat and entire as in, Nymphaea and Nelumbo (Fig. 4.3) with their, upper surfaces coated with wax; their petioles, are long, flexible, and often covered with, mucilage. In Eichhomia (Fig. 4.2), and Trapa, (Fig. 4.3) petioles become swollen and, spongy., (2) Emergent forms as Ranunculus and Sagittaria, (Fig. 4.6) show heterophylly with submerged,, floating, and aerial leaves., (3) Submerged leaves are generally translucent., Flowers and seeds. These are less common, in submerged forms. Where flowers develop, seeds, ·, are rarely formed., , Anatomical Features, Roots, , t, , in, tissues, of various, The distribution, roots of hydrophytes, in general, becomes clear, from Figures 4.7 and 4.8 showing transverse, sections of roots of Potamogeton and Eichhomia, respectively. It may be concluded from these, figures that:, (I) Cuticle is either completely absent or, if, present it is thin and poorly developed., (2) Epidermis is usually single-layered made up, of thin-walled parenchymatous cells., (3) Cortex is well developed, thin-walled and, parenchymatou s, major portion of which is, occupied by well developed prominent air, cavities - the 'aerenchyma' which offers, resistance to bending stress, increases, buoyancy and allows a rapid gaseous, exchange., (4 ) Vascular tissues are poorly developed and, least differentiated in submerged forms, as, Potamogeto11 (Fig. 4.7) with thin-walled, elements. In xylem. vessels are less common, tracbeids being generally present. In floatin~, , (BC-4), , '-. 8 .d, P1 ermis, , ::-..epidermis, , ", , outer cortex, , air chambers, (lacunae), , I, , Fig. 4.7. T.S. root of Potamcgeton pectinatus (submerged, hydropbyte). Note the absence of root hairs and cuticle;, undifferentiated broad cortex with air chamber.;, vascular, tissues poorly developed, represented mainly by phloem:, I, lack of mechanical tissues., , forms as Eichhomia (Fig. 4.8) they are, comparatively differentiated to some extent, However, in emergent forms as Ranuncu/11s, and Typha etc., vascular elements are, comparatively much distinct and well, developed., (5) Mechanical tissues are generally absent excepl, in some emergent forms, as Typha where piih, cells are sclerenchyrnato us., , Stems, Distribution of various tissues in stems of, hydrophytes becomes clear from transverse section, of stem of Hydrilla (Fig. 4.9). It may be seen, that:, (1) Cuticle is either absent or poorly developed, and thin., (2) Epidermis is usually single-layered made up, ceUs., ., d, parenchymatou s, thm-walled, of, However, rhizomes of Nymphaea an, , la"';,,.-;~- endodermis, , pericycle, xylem, , 4 8 T S root of Eic/1/romia (floating-leaved hydrophyte). Note., b . and cuticle· undifferentiated well developed, . .f, "' resented, ·, ., ', the absence o root au:s, cortex with abundance of aerenchyma; mccharucal nssucs P, only by xylem elements., , Fi, , g. .., , Nelumbo show well-developed epidermis. In, emergent forms as Typha, cuticle as well as, epidermis are generally well developed. ., 3, < ) HyPodermis is completely absent mand, Hydrilla, as, forms, submerged, Potanwgeton. However, in floating and, emergent forms, it may be present as thin(4) Walled parenchyma or collenchyma., Cortex is well developed, thin-walled an_d, ~hymatou s, extensively traversed by air, Cllvi.ties as in roots. Cells of cortex generally, thus, are, and, chloroplasts, , photosynthetic. In some, as Nymphaea, there, are found large number of vascular bundles, ., scattered in the cortex., (5) Endodermis is generally distinct, especially, in rhizomes and similar organs., ( 6) Vascular bundles generally lack bundle, sheaths. Vascular elements are thin-walle~~, However,, Ii ified elements being absent. I·, r elements, gn, emergent forms as Typha, vascu a . d and, are compa-ratively well differentiate, bsent., developed., (7) Mechanical tissues are usually a

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Water Regimes ana r=c;u1uy1c;a1 Aaaptations ,, , - -~68~----- ----- --- - -;-=-=-=-=-=-=-=-=~~~i-;:-=-=~;~~~~i~~-;.::, , water Regimes and Ecological Adaptations, 69, , ·n different, of, 1n their internal structure, Ieaves I, hydropbytes show variations. However, so::: of, ., the anatomical features are common to_ m, the leaves. Distribution of different assues :, leaves of hydrophytes would become_ clear, 410 411 and 4.12 showmg veh I ·, ., F1gures • , . ·, of leaves of . Anoe Fans,, transverse sections, Potamogeton and Nymphaea respecnvely. rom, these we may conclude that in leaves:, ( 1) Cuticle is usually absent in submerged, forms as Anacharis and . Potamogeton, (Figs. 4_IO, 4.11). In floatrng forms as, Nymphaea (Fig. 4.12) it is poorly _deve!oped, confined only to upper side, and 1s thin. In, ., emergent forms also it is thin., (2) Epidermis is single-layered, made up of thinwalled cells with abundance of chloroplasts., (3) Stomata are completely absent in submerged, leaves as Anacharis and Potamogeton, , :~al, , epidermis, hypodermis, , sub-stomata!, chamber, palisade, spongy, ""1'"--'/"'.'Y.s-;i;:;;;<,-p arenchyma, , (Figs. 4.IO, 4.11). In floating forms as, Nymphaea (Fig. 4.12) stomata are confined, only to the upper surface of leaf, whereas in, emergent forms they are generaIJy found on, both surfaces of leaves., (4) Mesophyll is undifferentiate d in submerged, leaves, where i t is generally single-layered, as in Potamogeton (Fig. 4.11). In Anacharii, (Fig. 4. IO) also it is thin and undifferentiated., In floating leaves as Nymphaea (Fig. 4.12),, it is, however, differentiated into palisade and, spongy parenchyma with well-developed air, cavities. In emergent leaves, mesophyll is well, differentiated with air cavities., (5) Vascular tissues are very much reduced and, sometimes difficult to be differentiated info, xylem and phloem as in leaves of submerged, forms like Anacharis (Fig. 4.IO). Wherever, 2, differentiated as in Nymphaea (Fig. 4.! /·, xylem elements are thin-walled, phloem beifl!, ·al ]eaves., ., well developed. However, rn aen, 11, vascular elements are comparatively we, differentiated with vessels in xylem., , ooo, , Oo, 00, , oo, 0, 0 00, , I, , ~ ., , g, , oo, ~o, , l' i,:::t,',f--%-:,1::,e~::A,~~:s.. trichosclereids, r epidermis, , xylem, vascular, bundle phloem, of vein { bundle sheath, , } vascular, cuna, metaxylem bundle, ~::t'-f::;;:::f-?''t'f-- - - - phloem of mid rib, , Fig. 4.U. T.S. Jeaf of Nymphaea (floating-leaved). Note, the thin cuticle; stomata being confined only to the upper surface;, thin,-walled q,idermal cells; abundance of air chambers in spongy parencbyma; absence of mechanical tissues (only sclereids, present); reduced vascular elements represented mainly by phloem, xylem being much reduced., , clereid, air chamber, loem}vascular, lem bundle, , meso hyll cells, , upper epidermis, , / Flg. 4.9. T.S. stem of Hydrilla (subme, Note, the absence of cuti 1 .. . rged hydrophyte), undifferentiated conex with c_ e, lbtn-walled epidennis;, air chambers· a bund ance of, •, I, •, thm-walled elements· abse, nceofmh ', ·•, composed "". amcal tissues;, I reduced vascul&r clements, chiefly, ', ., . . of phioem,, hy, represented only, ;' xylem be,ng, a cavity m the centre, .- . - -, , air chamber, (lacuna), , Fig. 4.10. T.S. leaf of Anacharis (submerged). Note, the, absence of cuticle and stomata; undifferentiated mesophylJ, represented by single-layered parenchyma; reduced vascular, tissues represented by thin-walled cells in the centre·, '/, absence of mechanical tissues., , 0 o~ 0 o 0 0, , go, , 0000, , O O, , O, o, , 0, , 0, , o, , oO, , lower epidermis, )'{, , , -- -- - - - - -- -------:-.-:-- shown 1f, Fig. 4.11. T.S. leaf ( only lateral wing portwn abSC , c< ~' 1, th, Po'.amogelon pusil/us (submerged). ~otc, e_; le-l•Ye~, undifferenuated, stomata,, cuticle and, mesophyll between two epidermal layers., , 511, , g, , d) Note the absence of cuticle; thin-walled epidermal, ., Fig. 4.13. T.S. petiole of Nymphaea (floaung-Ie~e a ·few la~ers of collenchymatous hypodennis; abundance, cells; reduced mechanical tissues represented only y O f hloem xylem being represented by lacunae., nd, ', P, of aerenchyma; vascular elements with abu ance

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1, 7, P, ::;--:::, ::~:~::, ---;;;~, ~-~--------~, o, ~, --~, Water Regimes and Ecological Ada, , 0, , at, ,r:, , Vascular and mechanical tissues, developed and well differentiated., h, (9) They may s ow temporary wilting dun., noon hours ., (8), , (6) Mechanical tissues are absent., •, (7) The pe tioles. wherever well develo~. as m, , internally, (F·g, L1 4 13) also possess, · I, . ., · ·, Nvmp,..,ea, various tissues charactensuc of a typ1ca, hydropbyte, i.e., an abundance of a~n~hym_a., thin-walled cells, lack of different.Jauo~ m, vascular tissues and absence of any hgnified, mechanical tissues., , the, , MESOPHYTES, They are very extensive on the land surface. They, are such land plants which grow in moist habitats, and need well-aerated soils. They prefer soil and, air of moderate humidity and avoid soil with, standing water or containing a great abundance, of salts. In some respects they stand in between, the hydrophytes and xerophytes. Broad-leaved trees, growing in wet depressions, along lakes and rivers,, are mesophytes. They generally lack the special, structural and physiological adaptations found in, hydrophytes and xerophytes., The general morpho-anatomical features of, mesophyte are as follows:, ( 1) Root system is well developed. Roots are, generally fairly branched, with root caps and, root hairs., (2) Stems are generally aerial, solid and freely, branched., (3) Leaves are generally large, broad, thin and, varied in shapes; generally oriented, horizontally, green, without hair or waxy, coatings., (4) Cuticle in all aerial parts moderately, developed., (5) Epidermis well developed, without any hair, or waxy coatings and cells without, chloroplasts., (6) Stomata generally present on both, surfaces, of leaves. Guard cells show frequent, movements., (7) Mesophyll in leaves is differentiated into, palisade and spongy parenchyma, with many, intercellular spaces., , ~~, water Rionimes, , and Ecological Adaptations, , 71, , Oil the basis of their morphology, physiology, life cycle pattern, xerophytes are generally, and itied into the following three categories:, class, , 1. Ephemeral Annuals, , XEROPHYTES, The term xerophyte has been defined at;', interpreted variously. Morphological features ~, rates of transpiration have almost failed t;, explain the true nature of this group of plant;., They are sometimes loosely defined as 'plants of, dry habitats'. But if taken in this sense, most of, the mesophytes should be called xerophyte;, Daubenmire (1959) in his discussion on th:, group defined xerophytes as 'plants which gro,, on substrata that usually become depleted of, growth water to a depth of at least 2 decimetm, during a normal season'. Thus, in arid zones. all 1, plants not confined to the margins of streams or ', lakes have been considered as xerophy1es,, whereas in regions of heavy rainfall the cl:i.ss, would be represented only by shallow-rooted, plants of sandy soils, by plants of dry ridgetops,, and by algae, mosses and lichens which grow, on tree barks or rock surfaces etc. The II\Je, nature of xerophytism is not clearly understood., For example, it is difficult to decide whether J, xerophyte is really xerophilous and occurs onfy, in dry habitats and deserts, or is merely drought·, resistant. There are instances, for example, thal,, if desert plants are grown in soils with moderale, amount of water, they show better growth as 111, Anemisia fasciculata, Zygophyllum fabago auri, Centaurea solstitialis, the yield of planlS, increased to 1.5-2 times by increasing water·, holding capacity of soil from 40% to 60%Thus, such xerophytes are not xerophilous al, leaSt so far as the soil moisture is concerned,, Oppenheimer (1960), in a literature surve)'•, favours a much broader interpretation includuig, anatomical . a~:, morphological,, all . the., physiological modifications which may assiSt _tl, plant to cope with environmental water deficit., , also called as 'drought evaders' or, · an·d, d m, ', areescapers'. They are mostiy 1oun, Tuey ght, 'drOU Tuey are annuals, which complete their life, zones. .thin a very short period of 6-8 weeks or, ·, h, cycles wi, their small size and large s oots m, With, 1, to roots, they are well adapted to such, so. ., ·ths d, ·d d, relatton, habitats. They actually avo1 an not w1 tan, external, in, dryness, escape, thus, and, dry, dry seasons,, and internal environmen ts. Some do not prefer, to call them true xerophytes. Example~Argemo ne, ,nexicana, Solanum xanthocarpum, assia tora,, Tephrosia purpurea, etc., , 2. Succulents, They are the plants that suffer. from dryness in, external environment only. Therr succulent, fleshy, organs (stems, leaves, roots) serve as water-storage, organs which accumulate large amount of water, , during brief rainy seasons. In cacti moreover, the, root systems also become shallow. Their root, system is shallow, stem swollen and leaves thick,, leathery and succulent. Some of the examples are, Aloe, Euphorbia and Opuntia (Fig. 4.14) and, various cacti, Agave and Ceiba parvijlora. As the, succulents avoid drought, some prefer to exclude, them from true xerophytes. This is indeed a unique, mode of adaptation., In some of them, stems become succulent,, which are also called the 'fleshy xerophytes' as, in Opuntia and Euphorbia (Fig. 4.14). In such, xerophytes, cuticle is thick, and well developed, hypodermis is two-to-three layered, collenchymatous; cortex is also thick-walled with, chlorenchymatous cells, below which there is, present a prominent 'water-storage region' , whose, cells are thin-walled with a few intercelluJar, spaces. Those succulent xerophytes in which leaves, become fleshy; are also known as ' malacophyllous, xerophytes', such as Aloe (Fig. 4.14), Begonia,, Salsola, Bryophyllum, Agave, Yucca, Tradescantia, etc. Their leaves possess turgescent parenchymatous cells with thin walls. Asparagus and Ceiba, parvifolia store water in their roots., , Opuntla, · Aloe, , Euphorbla, , Fig. 4.14. Succulent xerophytes., , 00,

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----,..,lu,,uns, 78, ., s very well developed., Mechanical nssue, ., .d In, •, ., veral kinds of sclere1 s., including se ., developed, complex, Pi11us. there is we 11, transfusion tissue., ., 1 1, (3) In some non-succulent xerophytes . parncu ar y, as Ammophila and Agropyron, grasses4,? I A B) leaves become rolled and/or, (Fig. , ·- ', t, that the. stoma, fold eel .m sueh a manner, ·, . . . a, .dden position. thus mmumsm_g, occupy a hl, th, the rates of transpiration. Moreover., elf, epidennal cells remain mostly turgid. ., We have described in detail the vanous, morphological and anatomical features of each, of the three major ecological groups of plants,, hydrophytes, mesophytes and xerophytes. A, comparative account of the same is presented, in Table 4 . 1 also., , HALOPHYTES, They are a special type of xerophilous plants, which grow on saline soils with high, concentration of salts like NaCl., MgC\2 and, MgS04. Soils are physiologically dry. Their, osmotic pressure values are very high. Most of, them are succulents, their leaves are evergreen,, thin, small and leathery with water storage, tissues, thick cuticle and well developed palisade, , epistomatal, , chamber, , tissues. Most of them produce special type of, branched, negatively geotropic roots that corne, out of the mud surface to encourage the entry, roots are called, of oxygen gas. 111ese, pneumatophores which possess breathing porci, for gaseous exchange. Some of the halophytes, show vivipary i. e., germination of seeds before, they are shed from parent plant. The universal, feature of these plants is selective absorption and, tolerance of sodium chloride, and the ability to, grow in soils so saline that they are either, physiologically toxic to normal plants or impose, so serious an osmotic water stress that water, absorption is impeded. Plant cells are bailied in, a medium of high osmotic potential and thus, should maintain a higher vacuole osmotic, potential in order to avoid loss of water., Halophytic, communities, have, been, divided (Warming, 1909) into (i) lithophilous,, (ii) psammophilous, (iii) pelophilous, and, (iv) helophilous types, growing on rock and, stones, sand, mud, and swamp respectively., Helophilous halophytes have been further subdivided into (i) salt-swamp and salt-desert, and, (ii) littoral swamp-forest (mangrove) types, of, which the latter are most extensive, which occur, in all tropical seas, especially on flat, muddy, shores, where the water is relatively calm, as in, lagoons, inlets, estuaries etc. Soil is flooded with, water either permanently or at high tide. These, , stoma, , cuticle, , water Regime::;, •-•te, , T<au, , di /U, , c::1..,u1uy1ca1, , Adaptations, , 79, , ,t.J. Generalised morphological, a na tomical a nd, , Ph) siological fratu rrs, , ,.\~:1:.:ic:.~t~-:r_....,,uard cell, ---+---+-4--....L..--substomatal, chamber, , fie. 4.22. A pan (mainly epidermal, ., heavy deposition of, ., J of T. S. leaf of a succulent xerophyte to show thick cuucle,, cunn and cellnlose 00 outer walls of epidermal cells and stomala., , nr, , plants., , Mesophytes, Xerophytes, , Morphological, I. Excepting the emergent forms, roots, generally greatly reduced, even, absent : if present, unbranched, without root hairs., 2. Stem very much reduced, in some, modified into rhizomes, thin, delicate., 3. Leaves thin, narrow, linear, some, with long petioles and large lamina,, covered with wax or haris, in some, dissected into segments., , Anatomical, ]. Aerenchyma extensive almost in all, vegelative organs., 2. Cuticle generally absenL, 3. Stomala either absent, or if present,, only at upper surface or even nonfunctional., 4. Mesophyll, undifferentiated, into, palisade and spongy parenchyma., 5. Chlorophyll in addition to leaves also, in other parts of planL, 6. Epidermal cells thin-walled., 7. Lignified mechanical tissues lacking,, conducting elements very few, nonlignified., Physiological, , Habitats mostly deficient in oxygen, con~t, thus having an ability to, "'"PJre anaerobically, or have low, requirements., Special, oxygen, aerating organs are presenL, , littora1, vegetatt· swamp-forests, on, known, th, , •_.::. ·:;·., , lh, rC'e ecological ~roup,, , Byclropbytes, , 1. Root system well developed, ta, fibrous roots wilh root haris. P or, , 2 · Siem is rigid and stout., , fo,-.ati, ., .... onmtr, , .as, , form, , a, , 2. Stem . much, , 4. Palisade, well, developed, differentiated., 5. Chlorophyll mostly in leaves., , and, , 6. Epidermal cells thick., 7 · Meacbaoical and vascular tissues, well developed., Normal phys iological processes, wilh, temporary, willing, at, room, temperature., , characteristic, , e mangroves or mangrove, , opical and subtropical areas., In lndi, on SCash a, mangroves are very much prevalent, i\nt1~-- ores of Bombay and Kerala and in, -uanand N·, logged soi), icobar islands. They grow on waterswainpy ' whe~ habitat is characterised by sandy,, s~~ soils , high precipitation, high, ternPeraturc thrutnidity and almost no fluctuation in, ha10ph,,.oughout the year. The two common, .,...,. of thi, illld So111zerati s type are Rhizophora mucronata, Pneulllatoph, a. They produce still roots,, Xeroinorphicoresh and show vivipary. They show, c aracters as evident from the, , atrnOSpbe:\, , I. Root system generally very deep,, extensive, reaching deeper layer,; of, soil: several times larger than shoot., hard. woody., dwarfe<I,, , branched,, , 3. Leaves large, lhin, generally wilbout 3. sometimes underground., Leaves small. sometimes much, waxy surfaces., reduced to scales or modified into, spines, in some lealbery and thick, w,lb_ shining surface and waxy, coa11og. covered wilb hairs., I. Aereocbyma lacking., I., Aereochyma lacking., 2. Cuticle developed., _, 2 Cuticle thick, well developed., 3 . Stomata on one or bolb lbe surfaces. 3., Stomata less in number, generally, confined to lower su,faces of leaves,, sunken., , proper, , ... cutinised layer } outer wall of, ,·., id, I II, /, ::~cellulose layer ep erma ce, , or, , 4. Palisade generally on both sides of, leaves, cells and vacuoles small., 5. Chlorophyll mostly in stem and, Jeavcs., 6. Epidermal cells conspicuously thickwalled., 7. Mechanical and vascular tissues very, well developed., Most of lhe features directed to, reduce the transpiration rates;, ephemerals complete life cycle in, short period, High osmotic press=, (as much as 3 100 atms. in some, halophytes), and endurance of, desiccation., , anatomical characters of vegetative organs of, Rhizophora mucronata given below., , Roots, Roots are of two types, aerial and subterranean., The subterranean root m transverse section, (Fig. 4.23) shows:, (I) Several-layered cork., (2) Cortex, made up of star-shaped pr, stellate cells, connected wiili each other by, lateral arms. Cortical cells have peculiar, thickening ridges which are Iignified. Some, cells of cortex are filled with oil and and tannin., (BC-4)