Aquatic Botany, 5 (1978) 191--206 191 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

M O R P H O L O G Y , A N A T O M Y A N D H I S T O C H E M I S T R Y O F T H E A U S - T R A L I A N S E A G R A S S E S O F T H E G E N U S P O S I D O N I A K ( ~ N I G ( P O S I D O - N I A C E A E ) . I I . R H I Z O M E A N D R O O T O F P O S I D O N I A A U S T R A L I S H O O K F.

JOHN KUO and MARION L. CAMBRIDGE

Department of Botany, University of Western Australia, Nedlands, Western Australia 6009 (Australia)

(Received 6 February 1978)

ABSTRACT

Kuo, J. and Cambridge, M.L., 1978. Morphology, anatomy and histochemistry of the Australian seagrasses of the genus Posidonia KSnig (Posidoniaceae). II. Rhizome and root of Posidonia australis Hook. f. Aquat. Bot., 5: 191--206.

Rhizome branching of Posidonia australis Hook. f. occurs at irregular intervals in leaf axils, with one or no branch per axil. The cell walls of the rhizome epidermis and hypo- dermis are slightly thickened and lignified. Cortical cells have many starch grains. Fibre strands and vascular bundles are scattered among the cortical tissues. The cell walls of rhizome fibre cells consist mainly of cellulose and hemicellulose with a little lignin but the middle lamellae are heavily lignified. The fibres of both leaf sheath and rhizome resist decay and build up banks beneath the living seagrass. The rhizome stele has a central xylem surrounded by the phloem bundles which are finally surrounded by the endodermis. At the node region, one or a pair of roots may be produced. The thickened hypodermal walls of the root have a suberin lamella. The radial walls of the root endo- dermis are slightly thickened and have a Casparian strip. Both hypodermis and endo- dermis may restrict exchange of the water and solutes. A vascular system with weakly lignified tracheids is present in all roots.

INTRODUCTION

T h i s p a p e r d e s c r i b e s t h e m o r p h o l o g y o f t h e r h i z o m e a n d r o o t o f t h e A u s t r a l i a n seagrass Posidonia australis H o o k . f. a t t h e g ross a n d u l t r a - s t r u c t u r a l l eve ls , a n d c o m m e n t s o n t h e r e l e v a n c e o f t h e s e s t r u c t u r e s t o t h e o c c u r r e n c e o f t h e p l a n t o n s and s u b s t r a t e in t h e c o a s t a l m a r i n e e n v i r o n m e n t . T h e l e a f b l a d e a n d l e a f s h e a t h a r e d e s c r i b e d in an e a r l i e r p a p e r ( K u o , 1 9 7 8 ) . P. australis is o n e o f t h e m a j o r s p e c i e s o f seagrass f o r m i n g e x t e n s i v e sub- m a r i n e m e a d o w s in e m b a y m e n t s o f t h e s o u t h e r n A u s t r a l i a n c o a s t ( C a m - b r i d g e , 1 9 7 5 ) a n d is n o t a b l e f o r i t s c o n t r i b u t i o n t o f i b r e d e p o s i t s . D e p o s i t s o f m a r i n e f i b r e in S p e n c e r a n d St . V i n c e n t G u l f s in S o u t h A u s t r a l i a a re p r e s e n t in s u c h q u a n t i t i e s t h a t t h e f i b r e w a s m i n e d o v e r a l i m i t e d p e r i o d ( 1 9 0 5 - - 1 9 1 5 ) as a s u b s t i t u t e f o r j u t e f o r g ra in bags ( W i n t e r b o t t o m , 1 9 1 7 ) .

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Other uses described by Read and Smith (1919) include paper making and insulation.

Morphological studies on Posidonia roots and rhizomes were carried out by Sauvageau (1889), who described the anatomy of the vigorous and lig- nified rhizomes and adventitious roots of the Mediterranean species, P. oceanica (L.) Delile, and by Weber (1956). Den Hartog (1970) described the morphology of the rhizome of P. australis and commented on its mono- podial growth. Tomlinson (1974) drew attention to the incomplete know- ledge of shoot organization in seagrasses and stressed the importance of the rhizome for persistence of seagrass populations, proliferation depending on the activity of apical shoot meristems.

The functional importance of roots of submerged aquatics in uptake of solutes remains a matter of debate. The reduced vascular system and poor development of root hairs in some species have led to the suggestion that roots are unimportant for nutrient and water uptake (Sculthorpe, 1967). Tomlinson (1969) concluded that tracheids are absent from most of the root of Thalassia testudinum Banks ex KSnig and speculated that the roots have little significance in water movement and therefore are unlikely to be important in the absorption of water and ions. However, nutrient studies on aquatics in the laboratory have shown that roots may have a major role in the uptake of nutrients when compared with the leaves (e.g. Bristow and Whitcombe, 1971; Denny, 1972).

No previous studies on seagrasses have sought to examine the anatomical basis for nutrient uptake. This examination of P. australis roots provides anatomical evidence that the roots, despite their reduction, contain the necessary structures for solute uptake and translocation.

METHODS AND MATERIALS

Material for the rhizome branching study and for examination of gross morphology and fibre deposits, was collected from Cockburn and Wambro Sounds and Shark Bay, Western Australia, Spencer Gulf, South Australia, and Merimbula, New South Wales. Material for the histochemical and ultra- structural study was collected from Garden Island and Cockburn Sound, Western Australia, and prepared as previously described (Kuo, 1978).

RESULTS

Living rhizomes have been found up to 0.5--1 m below the sand surface, ranging in colour from pale pink near the apex to a reddish-brown in the older portion, which eventually disintegrates into coarse, dark fibres.

Studies being carried out on leaf growth and turnover indicate that intact rhizomes may be at least 20--30 years old, on the basis of the number of nodes and average life of leaf.

The rhizomes are laterally compressed, and have persistent scars at the

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junctions of the leaf sheaths. Leaf sheaths are borne distichously on the rhizome, and enclose the rhizome apex, as do scale leaves in other taxa. Senescent leaf sheaths remain relatively intact for 6--12 months after the death and abscission of the leaf blade, depending on the nature of the sub- strate and degree of microbial activity. Eventually, much of the tissue rots away leaving only a mass of pale fibres like goat hair surrounding the rhi- zome. Rhizomes are not bilaterally symmetrical about the plane of inser- tion of the leaf sheaths. This is most obvious in the position of the roots, which tend to arise adventitiously on the lower surface of the rhizome. Each node represents one leaf, and internodes gradually extend to their mature length after the death of the subtending leaf. Internode length is under en- vironmental control, being influenced by sand influx for vertically extend- ing rhizomes, and space for lateral expansion. The longest internodes, up to 7 cm, are produced in areas of high sand influx where the rhizome apex grows upwards, maintaining an approximately constant level relative to the substrate surface. Individual clumps resulting from seedling colonisation of bare sand expand laterally by the production of rhizomes with a series of long internodes. Internodes may reach a length of only 1 mm where sand influx is negligible, and this suppression of internode elongation seems to be correlated with reduced vigour of the shoots. Branching also affects internode length, the internodes formed prior to branch initiation being many times longer than those formed just after a branch.

Rhizome branching

Branches of the rhizome are formed singly in the leaf axil and at irregular intervals; the branching of the rhizome simulates a dichotomy, as the branch and parent shoot are the same size (Tomlinson, 1974). Branches are each ensheathed by a prophyll, a transparent structure of similar height and widt h to the leaf sheath, but distinguished by a rounded apex. The prophyll is the only true scale leaf on the rhizome and is borne adaxially, as is usual in monocots, opposed to the branch-bearing leaf and backing onto the parent axis. The new shoot enclosed by the prophyll is interpreted as a branch of the rhizome, as it shows limited development and generally does not branch again. The parent shoot is interpreted as the main axis, as it continues to grow and branch. Fragments of the rhizome, which do not include the growing apex, will not regenerate.

Rhizome anatomy

In a transverse section of a rhizome about 5--8 mm deep and 3--5 mm wide, different tissues can be recognized. The outermost is an epidermis, then a three-layered hypodermis, a multi-layered cortex of parenchyma cells and a central, star-shaped stele (Fig. 1). As in P. oceanica (Weber, 1956), fibre bundles can be seen as small, brown dots distributed among the

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Fig. 1. Transverse hand section of a P. australis rhizome internode. Note the distribution of vascular (V) and fibre (F) bundles and central stele (ST). Toluidine blue. x 32.

Fig. 2. Scanning micrograph of the surface of the P. australis rhizome epidermis. Note bacteria and other microepiphytes, x 900.

cortical tissues (Fig. 1). The rhizome surface is smooth, apart from bacteria and diatoms, which are often present (Fig. 2). The epidermal cells are elongate (Fig. 2). The cell walls of the epidermis, the two outer layers of hypodermis and the distal port ion of the third hypodermis are slightly thickened, stain green with toluidine blue (Fig. 3) and are intensely auto- fluorescent (Fig. 4) indicating they contain lignin. Some epidermal and hypodermal cells contain polyphenolic materials.

Cortical cells are large, with thin walls which stain purple with toluidine blue (Fig. 5), indicating that they contain pectin. The intercellular spaces and the outer port ion of the cell walls that face the air spaces stain more intensely with toluidine blue and PAS reaction (Figs. 5 and 6). Starch: grains are usually present in the cortical cells (Fig. 6) as described for P. oceanica by Weber (1956). Many fibre strands are present in the cortical tissues {Fig. 1), being made up of between 20 and 50 or more cells. The

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Fig. 3. Rhizome of P. australis. Slightly thickened epidermal (E) and hypodermal (H) cell walls (arrows) and the polyphenolic materials (P) are stained moderately with PAS reaction but the thin cell walls of cortical cells (CT) are stained intensely. X 240.

Fig. 4. Same field as in Fig. 3. Note the cell walls of the epidermis (E) and the hypoder- mis (H) and polyphenolic materials (P) in cortical cells (CT) are intensely autofluores- cent. X 240.

individual f ibre cell has a small lumen wi th a th ick wall, which stains purple wi th to lu id ine blue (Fig. 5), reacts in tensely wi th PAS (Fig. 6) and is strong- ly b i ref r ingent (Fig. 8), bu t no t au to f luo re scen t (Fig. 7). The wall appears to conta in cellulose and hemicel lulosic polysacchar ides , and very little lig- nin. The middle lamella o f these fibres is very dis t inct , staining green wi th to lu id ine blue (Fig. 5) and being weakly PAS posit ive (Fig. 6), bu t is inten- sely au to f luo re scen t (Fig. 7) indicat ing l ignification.

There is a cent ra l stele and eight or nine smaller vascular strands in the cor t ica l tissues (Figs. 1 and 9). The vascular bundles are similar to those in the leaf blade or sheath, and are also su r rounded by a layer o f thin-walled bu t lignified bundle-shea th cells. The x y l e m e lements are very weakly ligni- fied. The centra l stele is star-shaped in transverse sect ion (Figs. 1 and 9) with a cent ra l xy l em e l emen t and x y l e m fibres, b o th of which are th ickened , and wi th lignified walls. There are usually 12- -14 p h lo em bundles surround- ing the cent ra l x y l e m elements . A single layer of endode rmis sur rounds the stele. The s t ruc ture o f endode rma l cells o f rh izomes is the same as descr ibed be low for the roo t . Po lypheno l -con ta in ing cells are sca t tered in all tissues of the rh i zome , including the stele (Figs. 5, 6, 9 and 10).

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Fig. 5. R h i z o m e o f P. australis. Middle lamel lae are more in tense ly s ta ined t h a n t he cell wall p r o p e r o f the f ibre cells (F). The in te rce l lu la r spaces (ar rows) and the p o r t i o n s of the cor t ica l cell wall t h a t face air spaces are more s t rongly s ta ined wi th to lu id ine blue. P: p o l y p h e n o l i e mater ia ls . X 320.

Fig. 6. R h i z o m e o f P. australis. The in terce l lu la r spaces and p o r t i o n s (a r row heads ) o f the cor t ica l cell wall t h a t face air spaces are m o r e s t rongly s ta ined b y PAS reac t ion . The f ibre cell (F) walls are s t rongly PAS reac t ion posi t ive b u t the midd le lamel lae are on ly m o d e r a t e l y posi t ive. Some cor t ica l cells con t a i n small s t a rch grains (S), whi le o the r s have p o l y p h e n o l i e mater ia l s (P). x 320.

Root anatomy

Paired roots are usually produced laterally at a node from the stele of the rhizome. Root product ion is intimately associated with shoot development, since roots arise in acropetal order close to the rhizome apex. The roots penetrate through the cortical and epidermal tissues (Fig. 11) and then enter the substrate. They are up to 20 cm in length and 3 mm in diameter and become diffuse with age. When a roo t tip is damaged, a group of fine undulating roots (ca. 0.5 mm in diameter) is formed just behind the damaged region. The older por t ion of a roo t is light brown, the younger cream or white. Roo t hairs are small and not easily seen (Fig. 12). The ana tomy of main, branched and fine roots is similar. In longitudinal section, a roo t cap, meristem and mature regions can be recognized (Fig. 13).

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Fig. 7. Rhizome of P. australis. The middle lamellae (arrows) of fibre cells (F) are intense- ly autofluorescent, x 290.

Fig. 8. Rhizome of P. australis. All cell walls of the fibre cells (F) are strongly birefrin- gent. X 300.

R o o t cap region and mer i s t em The r o o t apex is covered by a p r o n o u n c e d cap (Fig. 13). Y o u n g cap cells

are small and thin-wal led. Mature cells have ra the r th ick walls and are vacuo- lated. S ta rch grains are m o r e a b u n d a n t in the basal than the distal pa r t of the cell (Fig. 15). On the marg in of the cap, the cells are highly vacuo la ted , wi th very li t t le c y t o p l a s m , and w i t h o u t s tarch grains. As in m a n y terrestr ia l r o o t mer i s t ems , the cells have thin walls and are r ich in c y t o p l a s m . The dif- f e r en t i a t i on of regions in the roo t s o f Thalassia has been descr ibed in deta i l ( T o m l i n s o n , 1969) and Posidonia australis shows the same pa t t e rn .

Mature region (Figs. 13 and 14) A t ransverse sec t ion o f a m a t u r e r o o t shows several d is t inc t regions

(Fig. 14). Epidermis : The wall is a u t o f l u o r e s c e n t (Fig. 17), weak ly PAS posi t ive ,

and stains green wi th to lu id ine blue (Fig. 18) indicat ing the p resence o f po lypheno l s .

t t . 0 Fig. 9. Rhizome of P. australis. In the rhizome stele region, the central xylem elements (X) are surrounded by the phloem bundles (PB). Note also the fibre bundles (F) in the cortical tissue. PAS reaction, x 13.

Fig. 10. Rhizome of P. australis. The fibre bundles (F) are usually found associated with the vascular bundles in the cortical tissue. PAS reaction. X 400.

H y p o d e r m i s : One or two dist inct cell layers lie just inside the epidermis (Fig. 16). The cell wall is th ickened and stains purple with toluidine blue (Fig. 18) and has a s t rong PAS positive react ion, indicat ing tha t it conta ins cellulosic and hemicellulosic polysaccharides . A dist inct sudan-posit ive layer is present towards the middle lamella. The layer also is au to f luorescen t (Fig. 17) and stains green with toluidine blue. E lec t ron micrographs (Fig. 19) show the layer to be osmiophil ic , with a similar appearance to the suberin layer in the r o o t o f terrestrial plants (e.g. Ferguson and Clarkson, 1976; T ippe t t and O'Brien, 1976).

C o r t e x : This has three dist inct zones (Fig. 14). In the ou te r cor tex , the p a r e n c h y m a consists of abou t 20 cell layers, the inner cells o f which are m u c h smaller than the outer . There is a lacunose middle cor tex which is

Fig. 12. Scanning micrograph of the surface view of a P. australis root. X 45.

Fig. 13. Longitudinal section of a mature P. australis root. The root cap (RC), meristem region (asterisk) and the mature elongating zone (ME) can be recognized. Toluidine blue. X 13.

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Fig. 11. Rhizome of P. australis. Section through rhizome node region showing the con- tinuity of the rhizome stele (ST) and root (RT) and the fibre bundles (F) in the cortical tissue. Toluidine blue. × 27.

O~

~ ° -t

~°

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Fig. 17. Cell wall of the P. australis root epidermis (E) and the middle lamellae (arrows) of the hypodermal cells (H) are intensely autofluorescent. × 360.

Fig. 18. An adjacent section to Fig. 17, showing that the thickened wall of the hypoder- mal cell (H) is stronger than the middle lamellae and that of the epidermal cell (E). Tol- uidine blue. X 500.

Fig. 19. Root of P. australis. Transmission electron micrograph of a portion of the hypo- dermal cell wall (W). The distinct suherin lamellae (arrows) consists of two layers in the middle lamella region. × 30,000.

Fig. 15. A portion of P. australis root cap region, showing starch grains (S) confined to the basal region of the young root cap cells. Spurr's resin and toluidine blue. × 445.

Fig. 16. Scanning micrograph of a mature P. australis root showing the arrangement of epidermis (E) and hypodermis (H) in the root. × 770.

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® Fig. 20. The radial walls (arrows) of the P. australis root endodermis are slightly thicken- ed. x 430.

Fig. 21. The radial walls (arrows) of the P. australis root endoderm cells are autofluores- cent. x 320.

wide and represented by a series of longitudinal air spaces separated by groups of collapsed, elongate cells. Sometimes the cells are seen to be forked or fused in transverse section (Fig. 14). The inner cortex is of 5--6 layers of small cells. Each cortical cell is thin-walled and stains an even purple with toluidine blue. The walls have numerous plasmodesmata. The thin peri- pheral cytoplasm is rich in mitochondria and endoplasmic reticulum.

E n d o d e r m i s : The endodermis which surrounds the stele is composed of small, compact cells with rather thin walls. The middle portion of the radial wall is slightly thickened, stains green with toluidine blue (Fig. 20) and is autofluorescent (Fig. 21). Thus, this portion is lignified and possesses a Cas- parian strip (Fig. 22).

S t e l e : The stele contains all the vascular bundles of the root and the pericycle is not distinct (Figs. 20 and 21). There are four to five sieve tubes per bundle, and the structure of the sieve tubes, sieve plates and sieve areas is similar of that of the leaf blade and sheath (Kuo, 1978). The xylem has tracheids with poorly lignified walls (Fig. 23). The vascular parenchyma cell walls are thin, but the cytoplasm is rich in mitochondria, endoplasmic reti- culum and Golgi bodies.

Polyphenolic materials are sometimes present in the epidermis, hypo- dermis, cortex, endodermis and the parenchyma cells in the stele.

F i b r e a c c u m u l a t i o n

Both leaf sheaths and rhizomes produce fibre, so after a period of meadow

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: X XP

P M . . . . . . . .

, @ , _ @

Fig. 22. Root of P. australis. The slightly thickened portion of the radial wall of endo- derm cells (EN) with the homogeneous electron-dense appearance of the Casparian strip (CS). The portion of plasmalemma (PM) can be distinguished in this region, x 45,000.

Fig. 23. Xylem element (X) of a P. australis root. Xylem walls are not thickened, and some portions of the walls are hydrolysed (HW). Xylem parenchyma cells (XP) are rich in cytoplasm, x 7,000.

d e v e l o p m e n t the leafy shoo t s are carr ied above the mesh of f ibre, the in- ters t ices filled wi th sand and the ca lcareous skeletal r ema ins of animals and algae once res iden t in the m e a d o w . The pers is tence o f the f ibres is i l lus t ra ted b y the f ac t t h a t w o r m s , bu r rowing mol luscs and c rus taceans m o v e t h r o u g h at least the u p p e r p o r t i o n o f the mesh , p r o b a b l y turn ing over the sed iment . Despi te this ac t iv i ty , the f ibres ma in t a in their f o r m and preserve the essen- t ial f ea tu res of the depos i t s .

F ibres co l lec ted f r o m the P. a u s t r a l i s m e a d o w s (0.5 m deep) in Cock- b u r n Sound , Western Austral ia , consis t o f two kinds, or ig inat ing f r o m the shea th and r h i z o m e and being pale and da rk in co lour , respect ive ly . Each

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fibre is, in fact, a part or all of a fibre bundle as seen in a cross-section of the leaf sheath (see Figs. 26 and 27 in Kuo, 1978) and the rhizome (Fig. 1). The fibres vary in length from 5 to 20 cm and in diameter from 0.05 to 0.12 mm. Fibres originating from rhizomes appear coarser in texture and have an undulating surface. According to Read and Smith(1919), Posidonia fibres from Western Australia appear to possess the same main characteristics as the South Australian material but the filaments from the Western Australian sample were somewhat weaker.

DISCUSSION

Importance o f the rhizome to population persistence

Although P. australis produces seeds regularly and seedlings are common, the meadows persist as dense stands of underwater vegetation only as a result of rhizome growth and branching, corresponding to Tomlinson's (1974) concept of meristem dependence. No new growth from dormant meristems has been observed, so that the population is maintained only by the activity of the shoot apical meristems and the extent to which rhizomes can multiply by branching.

P. australis reaches its maximum development in relatively sheltered em- bayments in situations with continued sediment influx. Conditions fa- vouring rapid upward growth of the rhizome are preferred, which seems to relate to the strong monopodial growth.

Rhizome and root structure related to nutrient absorption and transport

The roots of Posidonia have features which are similar to those recorded for other submerged plants in that they have somewhat inconspicuous root hairs and little lignified xylem as compared with terrestrial species (Scul- thorpe, 1967). Because tracheids and vessels are inconspicuous and little lignified, some workers have been led to discount their function in seagras- ses. There is no doubt that the vascular system is present in leaf blade and sheath (Kuo, 1978) and also in the rhizome and root system of P. australis. Although there is little lignification in the xylem elements of a seagrass, the xylem may be as effective in water and ion movement as in the xylem of a terrestrial plant.

The sudanophilic layer in the root hypodermis has also been repor- ted from Thalassia testudinum (Tomlinson, 1969). The function of this layer is not well known. In terrestrial plants, Ferguson and Clarkson (1976) claimed that this layer in the root of Zea mays L. appears to severely restrict the translocation of both calcium and potassium. On the other hand, Tippett and O'Brien (1976) have suggested that the corresponding layer in the root of perennial dicotyledonous Eucalyptus obliqua L'Herit. and Eucalyptus st ]ohnii R.T. Bak. may restrict outward movement of water. The suberized

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hypodermis and endodermis in P. australis root may serve a similar purpose in restricting water and solute exchange. This may account for the findings that roots and rhizomes of Zostera marina L. absorbed less phosphate than leaves and stems (McRoy and Barsdate, 1970). The sudanophilic layer of the root, and the lignified epidermis and hypodermis of the rhizome, may also prevent the invasion of micro-organisms.

The accumulation of starch grains in the parenchyma cells of rhizomes suggests that these may also have an important role in carbohydrate storage, as in the rhizomes of many other submerged plants (Sculthorpe, 1967). It is not yet known if the rate of starch accumulation in the rhizome of Posi- donia australis varies with the seasons or physical environment, or is related to the growth of the seagrass.

Fibre structure related to fibre accumulation

In some areas, fibre deposits occur both beneath living seagrass banks and under sand dunes bordering the coast. The depth and fibre content of the accumulation appear to depend upon the local conditions of sediment influx which affect the upward growth of the rhizome apex. One of us (M.L.C.) has observed fibre accumulations several metres thick in the region of Pt. Broughton, Spencer Gulf, South Australia. These deposits relate to the growth of the banks since the rise in sea level associated with the Flan- drian transgression 8,000--4,000 years B.P.

Marine fibres contain lignin and cellulose {Winterbottom 1917; Read and Smith, 1919) but the percentage of cellulose is lower than that of most fibres of non-marine origin (Winterbottom, 1917). Delignified Posi- donia cellulose is not significantly different from cellulose of other plants (Bell, 1952). The accumulation of fibre deposits seems to be a result of rapid upward growth of rhizomes and resistance of fibres to decay. Bell (1952) considered that this resistance to decay may be associated with the manner in which the fibres are impregnated with lignin. Non-lignified paren- chyma cells of rhizomes and leaf sheaths may be lost soon after tissue dies, while the lignified fibre strands remain intact. Lignin not only acts as a waterproofing agent, but under certain conditions it has, like suberin and cutin, a resistance to decay (Clowes and Juniper, 1968). Lignin apparently acts here as a physical barrier delaying polysaccharide hydrolysis. Our studies showed that the middle lamellae in the rhizome and leaf sheath fibres are equally lignified, but the fibre cell walls in the sheath are more lignified than those in the rhizome. Thus the sheath fibres are the more likely source for the accumulations of marine fibre.

ACKNOWLEDGEMENTS

The authors wish to thank Associate Professor A.J. McComb for his critical reading of the manuscript and many encouragements. The senior

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a u t h o r was s u p p o r t e d b y a resea rch f e l l owsh ip f r o m the U n i v e r s i t y o f Wes te rn Aus t r a l i a .

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