Fibre dimorphism: cell type diversification as an evolutionary strategy in angiosperm woods

24 Pages·2013·5.64 MB·English

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Botanical Journal of the Linnean Society, 2014, 174, 44–67. With 9 figures
Fibre dimorphism: cell type diversification as an
evolutionary strategy in angiosperm woods
SHERWIN CARLQUIST* FLS
Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, CA 93105, USA
Received 15 May 2013; revised 4 August 2013; accepted for publication 14 August 2013
Dimorphic fibres in angiosperm woods are designated when zones of two different kinds of fibres can be
distinguished in transverse sections. The usage of most authors contrasts wider, thinner-walled, shorter (some-
times storied) fibres with narrower, thicker-walled fibres that have narrower lumina. The wider fibres can be
distinguishedinlongitudinalsectionsfromaxialparenchyma,whichusuallyconsistsofstrandsoftwoormorecells
each surrounded by secondary walls (and thus different from septate fibres). This phenomenon occurs in some
Araliaceae, Asteraceae, Fabaceae, Myrtales (notably Lythraceae), Sapindales (especially Sapindaceae), Urticales
andevensomeGnetales.Additionalinstancescandoubtlessbefound,especiallyifinstancesofwidelatewoodfibres
together with narrow earlywood fibres are included. There is little physiological evidence on differential functions
of dimorphic fibres, except in Acer, in which hydrolysis of starch in the wide fibres is known to result in transfer
of sugar into vessels early in the growing season. Starch storage in axial parenchyma may, in a complementary
way, serve for embolism reversal and prevention and thus for maintenance of the water columns. Crystalliferous
fibres(Myrtales,Sapindales)canbeconsideredaformoffibredimorphismthatdeterspredation.Gelatinousfibres,
often equated with tension wood, can also be considered as a form of fibre dimorphism. The evolutionary
significance of fibre dimorphism is that a few small changes in fibre structure can result in the accomplishment
of diversified functions. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014,
174, 44–67.
ADDITIONAL KEYWORDS: Acer – aerating cells – axial parenchyma – crystalliferous fibres – gelatinous
fibres.
INTRODUCTION this definition woods in which earlywood fibres corre-
spond to the wider fibres, with narrower fibres in
The phenomenon of fibre dimorphism was first
latewood. A large proportion of instances of fibre
describedinwoodofhelianthoidAsteraceae(Carlquist,
dimorphism involve living fibres, either septate or
1958), and subsequently cited as a product of imper-
nucleate, but without septa. This cursory description
forate tracheary element evolution (Carlquist, 1961).
doesnotincludethefullvarietyoneobserves,andthe
The concept has since been readily accepted, and has
present account is designed to characterize fibre
been recorded in wood anatomical monographs of
dimorphismmorefullysothatthephenomenoncanbe
familiesandgeneraofMyrtales,SapindalesandUrti-
noted and mentioned more frequently.
cales,asnotedindetailbelow,butislikelytobefound
In searching for diversity of expressions of fibre
more widely. In the usual sense, fibre dimorphism
dimorphism, two other manifestations must inevita-
consists of coexistence of zones of wide, thin-walled,
bly be considered. Crystalliferous fibres are pertinent
shorter fibres (usually libriform fibres, occasionally
in this respect, and have been described for several
fibre-tracheids)andzonesofnarrower,longer,thicker-
families of Myrtales. An expanded consideration of
walledfibres.Thesezonesmaynotcorrespondatallto
crystalliferous fibres and similar crystalliferous fibri-
latewoodandearlywood.However,onemayincludein
form cells in wood is an additional concern of the
present study. Likewise, gelatinous fibres (character-
*E-mail: [email protected] istic of tension wood) and similar fibres with
44 © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
FIBRE DIMORPHISM IN ANGIOSPERM WOOD 45
differentiation between inner- and outer-wall layers of view. When examining a transverse section,
in fibriform cells should be included in the concept of however,widelibriformfibres(orfibre-tracheids)may
fibre dimorphism. resemble axial parenchyma, and examination of lon-
Fibre dimorphism can range from subtle to promi- gitudinalsectionsisnecessarytodistinguishbetween
nent as seen in wood sections. To introduce the topic, wide, thin-walled libriform fibres and axial paren-
the characteristics that may qualify under the rubric chyma strands. Radial sections are perhaps most
of fibre dimorphism are each discussed. This is fol- useful in this respect. Tangential sections, however,
lowed by a systematic section, in which genera that are required when one is deciding whether storying
exemplify these characteristics are described and occurs in a given wood. Thus, the typical assemblage
illustrated in detail. The full extent of fibre dimor- of transverse (cross), tangential and radial sections
phism in angiosperm woods cannot be presented at thatonecommonlyseesonpermanentslidesofwoods
this point. Wood of only a small fraction of woody is a requisite. Such sections, made with the typical
species has been collected to date, and study of all of methods by means of sliding microtome techniques,
those collections is not feasible. Before I explore account for the bulk of the collections cited below.
angiospermsfurtherforfibredimorphism,wemustbe Although sections made from dried wood specimens
aware of the range of characteristics that have thus can be entirely satisfactory in many cases, additional
far been reported. Most angiosperm woods have important information (e.g. occurrence of nuclei and
monomorphic fibres (=monomorphic imperforate tra- starch) can be obtained reliably only from liquid-
cheary elements). In certain families, additional preserved material. Comparisons of liquid-preserved
examples are likely to be discovered once workers and dried wood specimens of a given species often
become familiar with the appearances cited here. showdisappearanceoralterationofstarchduringthe
Some preliminary patterns of systematic occurrence drying process because of hydrolysis and fungal and
are evident and can be mentioned, however. Fibre microbial action. For liquid-preserved material in
dimorphism in its various manifestations has arisen which thin cell walls are prevalent, the paraffin
independently in a number of clades. methods described by Carlquist (1982) have been
Fibre dimorphism can be interpreted in terms of followed.
wood physiology and mechanics, together with other The term ‘fibre’is used throughout this paper as a
features of any given wood. Fibres can be distin- synonym for ‘imperforate tracheary element’. Most of
guished from axial parenchyma in longitudinal sec- the species studied have libriform fibres; a few have
tions (in a small number of species, there can be fibre-tracheids, and none was observed to have trac-
admixture of the two cell types), and the probable heids. The correlation with libriform fibres is strong,
physiological differences between axial parenchyma because nearly all instances of living (including
andwidefibrescanaccountforwhyfibredimorphism septate) fibres involve libriform fibres. Living fibres
should have evolved in a number of woods, rather have contents with potential physiological value and
thansimplyanincreaseintheamountofaxialparen- thereby evolutionary possibilities of more than a
chyma.Dimorphismandpolymorphismhaveoccurred mechanical nature. Fibre dimorphism in the case of
in several cell types. One can point to vessel origin gelatinous fibres (non-lignified fibres), however,
from tracheids as a major instance of dimorphism in usually does not involve living fibres.
a cell type, resulting in division of labour. Dimor- The collections studied are as follows. Araliaceae:
phism in wood cells (vessels, tracheids, fibre- Aralia spinosa L., USw-12014. Asteraceae: Dubautia
tracheids) has occurred repeatedly in angiosperm menziesii (A.Gray) D.D.Keck, Carlquist H17 (UC);
woods (e.g. coexistence of vasicentric tracheids and D.platyphylla (A.Gray) D.D.Keck, J. W. H. 19188,
libriform fibres as a result of tracheid dimorphism, 1948, University of Illinois; D.raillardioides Hillebr.,
Carlquist, 1988; vessel dimorphism in lianas, Carlquist H16 (UC); Wilkesia gymnoxiphium A.Gray,
Carlquist, 1985). Such repatterning by means of cell Carlquist H10 (UC). Burseraceae: Santiria laevigata
type diversification represents a salient feature of Blume, Yw-19880. Combretaceae: Combretum eryth-
wood evolution, and probably accounts not only for a rophyllum Sond., cultivated at the Vavra Estate of
considerable portion of the amazing amount of phyl- (UCLA) C.farinosum Kunth., Henrickson & Christ-
etic change that has occurred in angiosperm woods, man 2101 (RSA). Fabaceae: Acacia dealbata Link,
but also the physiological success of various clades. cultivated at the Vavra Estate (UCLA); A.urophylla
Benth. ex Lindl., Carlquist 5563 (RSA). Fouquie-
riaceae: Fouquieria splendens Engelm., stem SJRw-
MATERIALS AND METHODS
14358; root Henrickson 21437 (RSA). Moraceae:
Fibre dimorphism is conspicuous in wood transverse Maclura pomifera (Rob.) C.K.Schneid., Utrecht
sections because wall thickness, lumen diameter and UN-262; Morus rubra L. Ripon W-252. Onagraceae:
cell diameter are most easily discerned in this plane Diplandra lopezioides Hook. & Arn., Breedlove 8052
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
46 S. CARLQUIST
(DS – CAS); Fuchsia boliviana Carrière, UCBBG phism. I have described here more conspicuous and
49.815;F.macrostemmaRuiz&Pav.,UCBBG49.806; thus easily illustrated instances of fibre dimorphism,
Hauya elegans DC. subsp. cornuta (Hemsl.) butthereare,naturally,afewtransitionalcases.The
P.H.Raven & Breedlove, Breedlove 6432 (DS – CAS); content of this essay essentially covers types and
Pseudolopezia longiflora Rose, Breedlove 8044 (DS – degrees of departure from fibre monomorphy.
CAS).Oliniaceae(=PenaeaceaesensuAPGIII,2009):
Olinia cymosa Thunb., Carlquist 4599 (RSA); Penae-
aceae:PenaeacneorumMeerb.,Carlquist4740(RSA). GELATINOUS FIBRES
Punicaceae:PunicagranatumL.,cultivatedatFranc-
Gelatinous fibres are usually equated with reaction
eschi Park, Santa Barbara, CA. Rutaceae: Evodia
wood:inwoodyangiosperms,reactionwoodisconsid-
cucullata Gillespie, SJRw-28318. Sapindaceae: Allo-
ered tension wood. The ‘gelatinous’ secondary wall
phyllus cominia (L.) Sw., SJRw-21859; Arytera brack-
maycontaincontractilestrandsofcelluloseinaback-
enridgei (A.Gray) Radlk., SJRw-18648; Cupania
ground of pectic compounds or other compounds with
pseudorhus Rich., SJRw-21855; Guioa subfalcata
hydrophilic properties; lignin in lignified fibres has
Radlk., SJRw-28232; Paranephelium macrophyllum
theeffectofprovidingstrengththroughagglutination
King, SJRw-26876. Thymeleaceae: Daphne pseu-
of fibrils, whereas gelatinous fibres are capable of
domezereum A.Gray, KYOw-6459. Urticaceae: Nerau-
shrinkage with dehydration of the pectic background
dia melastomatifolia Gaud., USw-15342; Urtica
(Du & Yamamoto, 2007; Bowling & Vaughn, 2008).
dioica L., Hope Ranch Park, Santa Barbara, CA,
We recognize gelatinous fibres in wood because of
Carlquist s.n.
their wall characteristics: the secondary walls are
thick, sometimes almost occluding the lumen
MODES OF FIBRE DIMORPHISM (Fig.1B,nlf).Shrinkagepatternsappearinsecondary
walls in sections that have been dehydrated, as in
Delineating the concept of fibre dimorphism depends
most permanent slides. Safranin tends to stain ligni-
on development of criteria for what we accept as
fied fibres more deeply (Fig.1B). If a counterstain is
manifestations. The concern goes beyond nomencla-
used, the gelatinous secondary wall tends to absorb
ture, because the various kinds of fibre dimorphism
the counterstain preferentially, and we see this as
represent evolutionary strategies, even though we
darkerbandsofgelatinousfibresinthereactionwood
may not be able to say with certainty what some of
of various angiosperms (Fig.6D, E). Little attention
those strategies are. I am taking the viewpoint that
has been paid to the longevity of gelatinous fibres in
we must begin with the premise that any instance of
comparisonwithlignifiedfibresinangiospermwoods.
co-occurrence of more than one type of fibre in sec-
Gelatinous fibres may not be entirely equivalent to
ondaryxylemmustbeexaminedasapossiblekindof
tension wood in angiosperms. The occurrence of
fibre dimorphism.
gelatinous fibres in wood of relatively non-woody
angiospermssuchasOnagraceaeleadsonetosuspect
MONOMORPHIC FIBRES that the two terms should not be used synonymously
(Carlquist, 1977). Gelatinous fibres are usually found
In transverse sections, fibres can be distinguished
inbands(Fig.6D,E),butmayalsobefoundscattered
from axial parenchyma (Fig.1A, ap) if the fibres are
within a matrix of other cells (Figs1B, 7D). In any
thick-walled.Iffibreshavethesamewallthicknessas
case, no survey of fibre dimorphism would be com-
axial parenchyma (e.g. Fig.1C), one must examine
plete without a consideration of gelatinous fibres.
longitudinal sections to be sure which cells are in
strands and are thus axial parenchyma, and which
are undivided cells, as in Figure1F (in a small
number of species, axial parenchyma cells are not LUMEN DIAMETER AND CELL SHAPE
subdivided into strands, as discussed below). Fibre The terms wide-lumen fibre and narrow-lumen fibre
lengths should be measured in macerations. The are used here. These dimensions can be expressed
monomorphic fibres of the root of Fouquieria splend- independently of wall thickness or cell length, but
ens (Fig.1A) contrast with the two kinds of fibres commonly there is some degree of correlation. In
(non-lignified fibres, nlf; and lignified fibres, lf – Daphnepseudomezereum(Fig.1C),thenarrowerlate-
which stain more darkly) in the stem. There is no wood fibres differ from the earlywood fibres in cell
clear decisive limit separating all instances of mono- diameter and lumen diameter, but all have approxi-
morphic fibres from all instances of dimorphic fibres, mately the same wall thickness. In Evodia cucculata
because there is natural variability in a cell popula- (Fig.1D), wider earlywood fibres (above) have both
tion. Fibre monomorphism is much more common in wider cell diameter, wider lumina and thinner
the world flora than are examples of fibre dimor- walls than earlywood fibres; they resemble axial
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
FIBRE DIMORPHISM IN ANGIOSPERM WOOD 47
Figure1. Examplesofwoodfeaturesrelatedtofibredimorphismsensulatofromtransversesections(A–E)andaradial
section (F). A–B, Fouquieria splendens. A, root wood; fibres are monomorphic. B, stem wood; non-lignified fibres
(gelatinous fibres) are intermixed with lignified fibres. C, Daphne pseodomezereum. Margin of a growth ring; libriform
fibresfluctuateindiameterandshapebutnotwallthicknesswithrespecttopositioningrowthring.D,Evodiacucullata.
Marginofagrowthring.Fibresinlatewoodareradiallynarrowerandthicker-walledthanthoseinearlywood.E–F,Morus
rubra.Libriformfibresaremarkedlywiderinearlywoodandresembleparenchyma,buttheradialsectionshowsthatthe
wide fibres are not subdivided as parenchyma strands would be. Key: ap, axial parenchyma; ew, earlywood; ewv,
earlywood vessel; lf, lignified fibre; lw, latewood; nf, narrow fibres; nlf, non-lignified fibre; nv+vt, narrow vessels+vasi-
centric tracheids; v, vessel; wf, wider fibres.
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
48 S. CARLQUIST
parenchyma, but have slightly thinner walls. Axial readily visible. I suspect that figures for fibre length
parenchymaoccursinthisspeciesintangentialbands insomestudiesmayhavebeenderivedfromsections,
three to six cells wide. because macerations are not specified in the materi-
In a wood with growth rings, such as Morus rubra als and methods sections of some papers.
(Fig.1E),thebackgroundcellsoftheearlywoodcould Even using macerations, results can be inconsist-
be either axial parenchyma or wide libriform fibres. ent. Wider fibres tend to be shorter; in Punica L.,
Longitudinal sections are needed to decide which of ‘fibres around the vessels are wider and shorter than
these is present. A radial section of this species other fibres and have rounded ends. Ratio of fibres to
(Fig.1F)revealsthatearlywood,widelibriformfibres vessel member length 1.7–1.9:1.’ (Bridgewater &
differ markedly from latewood fibres (left). In con- Baas, 1978). The mention of vessel elements,
trast, Maclura pomifera (Fig.9F, G) has wide fibres althoughincidental,doesillustratethatthewiderthe
intermixedwithtwo-celledaxialparenchymastrands. cell,thelessintrusiveandshorteritisasitundergoes
Latewood fibres most often appear somewhat flat- growth. If fibres are dimorphic in characteristics as
tened in a radial direction; that is, they are wider seen in transverse section, do they form a bimodal
tangentially (Fig.1C, D). Earlywood fibres tend to be curvewhenfibrelengthsareplotted?Theydonot,for
approximatelyisodiametricasseenintransversesec- several reasons. First, wider fibres are usually much
tions. Baas & Zweypfenning (1979) illustrated the less common than narrower fibres in a wood with
rounded shapes of the wider fibres of Lagerstroemia fibre dimorphism. Secondly, fibres of intermediate
floribunda Jack, which contrast with the more length are common, so that a curve of fibre lengths
angular shapes in the narrower fibres as seen in plotted against fibre diameters tends not to have
transverse sections. The wider fibres are associated peaks, but instead to have a broadened summit.
with intercellular spaces, lacking between narrower
fibres. Fibre dimorphism in Lagerstroemia floribunda
is not associated with growth rings. Workers may HOW FIBRES AND AXIAL PARENCHYMA DIFFER
ultimately wish to exclude instances of difference in
Implicitintheabovediscussionisthatwecanalways
fibre width related to growth rings from the phenom-
distinguish between axial parenchyma and fibres in
enon of fibre dimorphism, but there are genuine dif-
wood, and thereby place axial parenchyma out of
ferences between latewood and earlywood fibres, and
consideration. Can we? Both cell types are derived
inanumberofwoods,growthringsmaybeindistinct,
from fusiform cambial initials. Differences between
sothatadistinctionbetweengrowth-ring-relatedfibre
the two cell types that are commonly cited are as
dimorphism and non-growth-ring-related fibre dimor-
follows:
phismmaybedifficultorimpractical.Inanycase,the
overriding consideration may lie with evolutionary (a) Axial parenchyma is subdivided into strands of
interpretations, addressed in the last section of this cells; libriform fibres, even if living, are not.
paper, rather than in nomenclatural resolution. Livinglibriformfibresmaybeseptate,butcareful
examinationshowsthatcellsofaxialparenchyma
differentiateearlyinontogeny,sothateachcellin
WALL THICKNESS a strand is surrounded by a wall equally thick on
One might think that in fibres, if walls are thicker, all sides. Septate fibres have thicker walls,
luminaarenarrower.However,thefeaturesarenotso usually secondary, on axial surfaces, with only
obviously linked. For example, in Dubautia Gaudich. thin primary walls forming horizontal septa,
and Wilkesia A.Gray (Fig.2), narrower fibres have formed late in ontogeny of the fibre after the
walls that are not appreciably thicker than those of secondary walls have been laid down, that sepa-
the wider fibres. This applies also in Daphne L. rate the fibre into segments (Fig.5D, E). In some
(Fig.1C) and Morus L. (Fig.1E, F). Wall thickness is woods, such as Frankenia L., axial parenchyma
greater in narrow-lumen fibres than in wide-lumen cells are never subdivided (Carlquist, 2010). Non-
fibres in Paranephelium macrophyllum (Fig.4G). In subdivided axial parenchyma along with axial
comparing fibres within a wood, one should consider parenchyma composed of strands of two cells can
cell diameter, lumen diameter and wall thickness be found intermixed in the tangential paren-
independently. chyma bands of Erythrina L. and some other
Fabaceae.IntheFabaceae,axialparenchymadis-
tributions are distinctive and are not likely to be
FIBRE LENGTH mistaken for fibre dimorphism (which does occur
Fibre length should be measured on the basis of in some Fabaceae: Fig.3A–C).
macerations.Unfortunately,thatisoftennotdone.In (b) Each cell in an axial parenchyma strand is sur-
longitudinal sections, tips of fibriform cells are not rounded by its own primary and secondary
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
FIBRE DIMORPHISM IN ANGIOSPERM WOOD 49
Figure2. Fibre dimorphism in Hawaiian Asteraceae, shown in transverse sections (A, C, E) and tangential sections
(B, D, F). Growth rings are not present. A–B, Dubautia raillardioides. Fluctuation in libriform fibre wall thickness,
diameter and storying is present, but less conspicuous because of larger cell size. C–D, Dubautia menziesii. Fibre
dimorphismisconspicuousbecauseofdifferencesbetweenwidefibresandnarrowfibresinwallthicknessanddiameter.
Widerfibresareclearlystoried(atrightinD),narrowerfibresonlyvaguelyso).E–F,Wilkesiagymnoxiphium.Narrower
fibres have narrower lumina and greater wall thickness. Wider libriform fibres are easily distinguished from axial
parenchyma; the latter is always scantily vasicentric. Key: nf, narrower fibres; r, ray; wf, wider fibres.
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
50 S. CARLQUIST
Figure3. FibredimorphisminFabaceae(A–C)andBurseraceae(D–F)asseenintransversesections(A–E)andaradial
section(F).A–B,Acaciaurophylla.A,lowerpower,toshowsubtlefluctuationinapparentfibredensity.B,higherpowerview
tocontrastapatchofwiderfibres,above,withapatchofnarrowerfibres,below.C,Acaciadealbata.Earlywoodfibresare
muchwiderthanlatewoodfibres;axialparenchymaformsathinsheatharoundvessels,seenadjacenttothefibreatbottom.
D–F,Santirialaevigata.D,lowpowerview;therearenoapparentpatchesofwiderfibresandnarrowerfibres.Higherpower
view; between the arrow tips, there are wide fibres adjacent to vessels; axial parenchyma is very sparse in this species,
almostabsent,andislimitedtoacellortwoadjacenttovessels.F,arrowindicateswiderseptatefibreadjacenttovessel;
narrowerfibresarealsoseptate.Key:ew,earlywood;lw,latewood;nf,narrowerfibres;r,ray;v,vessel,wf,widerfibres.
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
FIBRE DIMORPHISM IN ANGIOSPERM WOOD 51
(usually present) wall, and the horizontal walls found in Punica (Fig.8C, D). Bridgewater & Baas
between adjacent cells of an axial parenchyma (1978) provided a scanning electron micrograph of
strand are pitted. These characteristics differ crystalliferous fibres in a longitudinal section of
from the thin primary walls of septa of fibres. Punica wood, clearly revealing the presence of sec-
Those septa stain distinctively and do not show ondary vertical walls. The crystals in this genus are
pitting. These distinctions are illustrated in separated by thin walls that can be presumed to be
Figures4D, E, 5E–G and 9B. primarywalls,orsepta,onthebasisofthicknessand
(c) Axial parenchyma cells frequently have thinner staining. One or two crystals per chamber are char-
walls than the fibres they accompany, and, if so, acteristically present (Fig.8D). Crystalliferous fibres
are easy to detect in transverse section. Such in Punica are tapered, like other fibres (Fig.8C).
contrasts are shown in Figure1A, B and D. The Bridgewater&Baas(1978)statedthatcrystalliferous
section shown in Figure1C exemplifies an fibres in Punica are shorter than non-crystalliferous
instance in which fibres have very thin walls and fibres.
cannotreadilybedistinguishedintransversesec- The categorization of other crystalliferous strands
tions from axial parenchyma. In such instances, found in wood may be more elusive than in the
longitudinal sections reveal whether these cells Punica example. Olinia Thunb. (Fig.8A, B), closely
aresubdividedintostrandsornot,acontrastthat related to Punicaceae, has crystals enclosed in fibri-
is usually present. formstrandsthatappeartohaveprimarywallsexclu-
sively. This is apparently true in other families, such
as Sapindaceae (Fig.4C–E). Because these strands
LIVING AND NON-LIVING FIBRES have the same shape and almost the same length as
Wolkinger (1970) listed species and genera of woody libriform fibres, they may be termed crystalliferous
angiosperms in which various authors have reported strandsandcited,alongwithcrystalliferousfibres,as
living fibres (including septate fibres). By ‘living an example of fibre dimorphism, although a case
fibres’, one connotes fibres in which protoplasts are could be made for terming the crystalliferous strands
alive when the fibres have reached their full length, as a form of axial parenchyma.
sothatinacurrentyearprotoplastsandnucleicanbe HauyaDC.(Onagraceae)haslargerprismaticcrys-
detected in fibres formed that year provided that tals (Fig.8E–G). These are located in libriform fibres
liquid-preservedmaterialisstudied.Notallinstances with secondary walls, although the distortion in cell
listedbyWolkinger(1970)havefibredimorphism,but shape due to their inclusion of large styloids masks
an appreciable number of them do, for a significant the cell shape. The styloid-containing fibres do taper
reason. If fibre dimorphism occurs, there is a division (Fig.8F, G, tt), indicating this identity. The crystal-
of labour between wide and narrow fibres, and that liferousfibresinHauyaarenotseptateandrepresent
division of labour involves a function reliant on lon- pronounced fibre dimorphism.
gevity in the wider fibres, such as starch storage.All
instances of septate fibres can be considered as prob-
able instances of living fibres. Septa in fibres do not STORIED FIBRES
survive maceration techniques well, but they usually The earliest examples to be cited as illustrating the
do survive sectioning techniques. Only liquid- phenomenonoffibredimorphismwereinthewoodsof
preserved materials can reliably document the occur- helianthoid Asteraceae (Carlquist, 1958). Dubautia
rence of nuclei in non-septate fibres, however. The spp. with shorter vessel elements (and, thus, with
presence of starch in a libriform fibre is to be consid- shorter accompanying libriform fibres), such as
ered evidence of living fibre presence in a wood D.menziesii (Fig.2C, D), tend to show storying more
sample. The present listing of living fibres in wood is conspicuously,butstoriedfibrescanbefoundinallof
minimal, and could be expanded greatly by further the Hawaiian madioid Asteraceae (Fig.2; Carlquist,
investigations. 1997, 1998a, b). In these and other helianthoid
genera, the shorter fibres are more clearly storied,
and longer fibres less conspicuously storied, in agree-
CRYSTALLIFEROUS FIBRES ment with the greater intrusiveness (and therefore
Crystal occurrence in wood is sometimes not men- greater irregularity in length) of longer, narrower
tioned in terms of the cell types in which crystals fibres. Storied wider fibres plus non-storied narrower
occur, and probably ray parenchyma and axial fibres were reported by Baas & Zweypfenning (1979)
parenchyma are the most common sites of crystal for Lagerstroemia calyculata Kurz (Lythraceae).
deposition. There are, however, crystals (generally Bailey (1923) demonstrated that in species with
presumedtobecalciumoxalate)incellsthatmustbe storied woods, storying increases with increase in
termed libriform fibres. A prime example of this is girthofthestem.Thus,specieswithfibredimorphism
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
52 S. CARLQUIST
Figure4. Fibre dimorphism in transverse sections (A, B, F) and radial sections (C–E, G) of wood of Sapindaceae.
A–D,Guioasubfalcata.A,lowpower,toshowcontrastbetweenwiderfibres(upperleft)andnarrowerfibres(lowerright).
B,highpower,toshowlocationofwiderfibres,narrowerfibres,axialparenchymaandacrystalliferousstrandinrelation
to a vessel. Axial parenchyma is scanty (three cells visible adjacent to vessel). C, low-power photograph to show axial
parenchyma adjacent to vessel and two crystalliferous strands. D, high-power photograph to show features similar to
thoseinC,plusseptatewidefibres.E–G,Paranepheliummacrophyllum.E,highpower,toshowwideseptatefibres(left),
narrowseptatefibres(right)and,betweenthem,acrystalliferousstrand.F,transversesectionshowingmarkeddifference
betweenwide,thinner-walledfibresandnarrow,thicker-walledfibres.G,radialsectionshowingcontrastbetweennarrow
fibres(left)andseptatewiderfibres(right),withsomeaxialparenchymastrandsseeninlongitudinalsectionadjacentto
a vessel. Key: ap, axial parenchyma; cs, crystalliferous strand; nf, narrower fibres; wf, wider fibres.
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67
FIBRE DIMORPHISM IN ANGIOSPERM WOOD 53
Figure5. Fibredimorphismintransversesections(A,C)andradialsections(B,D–G)ofSapindaceae.A–B,Allophyllus
cominia.A, margin of growth ring; wider fibres may occur in various places in a growth ring. B, narrow septate fibres
inlatewood,widerseptatefibresinearlywood,anaxialparenchymastrandnearavessel.C–F,Cupaniopsispseudorhus.
C, margin of growth ring (latewood at bottom); a notably wide zone of wider fibres adjacent to vessel. D, radial section
to show junction between earlywood and latewood. E, higher power of an area shown in D, to illustrate a single strand
of axial parenchyma, wider septate fibres and narrower septate fibres. F, wider fibres plus axial parenchyma and a
crystalliferous strand. G, Arytera brackenridgei, section to show thin-walled crystalliferous strands plus thick-walled
libriformfibresandaxialparenchyma.Key:ap,axialparenchyma;cs,crystalliferousstrand;ew,earlywood;lw,latewood;
nf, narrower fibres; wf, wider fibres.
© 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44–67