DOC-20220603-WA0028..pdf

Secondary xylem, Xylem, Paratracheal and apo tracheal parenchyma, vessels, tracheids, parenchyma,

1. Submitted by
Arsha T J
1 st Msc Botany

2. XYLEM
▪ThewordxylemisderivedfromtheGreekword‘Xylos’meaningwood.
▪ThistermwasproposedbyNageli(1858)
▪Itisoneoftheconductivetissueinplants.
▪Acomplextissue,composedofmanytypesofcells.
▪Mainfunction:Conductionofwater&minerals.
▪Additionalfunction:Providemechanicalsupport.
▪2types;Primaryxylem&Secondaryxylem.

3. ▪Primary xylem
▪Formedduringprimarygrowthoftheplant.
▪DerivedfromPro-cambium(apicalmeristem).
▪Consistof2parts;Protoxylem&Metaxylem.
▪Protoxylem:Firstformedxylem,containsfeweramountoftrachearyelements
&moreamountofParenchyma.
▪Metaxylem:Differentiateonlyafterprotoxylemdevelop.Containmore
trachearyelementsthanParenchyma.Theyarefunctionalintheplants
withoutsecondarythickeningthroughouttheirlifecycle.Inplantswith
secondarythickening,metaxylemarereplacedbysecondaryxylem.

4. ▪Secondary xylem
▪Formedfromvascularcambuim(lateralmeristem)duringsecondarygrowth.
▪Itswallsarethickenedduetothedepositionoflignintherebyrendering
mechanicalsupport.
▪Formannualrings.
▪Differentiationintosapwoodandheartwoodfoundinlargewoodytrees.
▪Usuallyvesselsremainpluggedwithtyloses.
▪SecondaryxylemProvidesadditionalstructuralsupportandwaterconduction
tissuesinshrubsandtrees.

8. COMPONENTS
Tracheids
▪Oneofthefundamentalcelltypeinxylem.
▪Elongatedtube-likecellwithbothendstapering.
▪Wallsthickinsomepalacesandthininothers.
▪Theyservebothaswaterconducting&strengtheningcells.
▪Nonlivingatmaturity.
▪MaturecellisemptywithoutProtoplast.
▪Cellswithsecondarycellwallwhichishighlylignified.
▪Cellsareangularorpolygonalincross-section
▪Endsoftracheidsofsecondaryxylemischisellike.
▪Lateralwallsandendwallsareprovidedwithpitpairs(facilitatelateralconductionofwater)
▪Waterandmineralpassagetakeplacethroughpitmembrane.

9. Vessels
▪Elongatedtubularstructurewithwidelumen.
▪Cheiefconductingelementinxylem.
▪Shortercellsthantracheids.
▪Cellsarenonlivingatmaturity.
▪CellsdeviodofProtoplastatmaturity.
▪Cellsarearrangedasseriesinendtoend,paralleltothelongaxisoforganinwhichthey
occur.
▪Componentsofvesselsarecalledvesselsegmentsorvesselelements.
▪Mainlypresentinxylemofangiosperms.
▪Secondarythickeningsimilartothatoftracheids.
▪Mainfunction:conductionofwaterandnutrients,mechanicalsupport(thicklignified
cellwall)
▪Vesselsbelievedtobeoriginatedfromtracheids.

10. ▪Trachearycellsaredividedintoseveraltypesaccordingtothetypesof
thickeningofwalls.
▪Annulartrachearycells–intheformofrings
▪Spiraltrachearycells–spiralthickening
▪Pittedtrachearycells–wallswhichareuniformlythickenedexceptforthin
placesintheformofpits.
▪Scalariformtrachearycells–ladderlikethickening
▪Reticulatetrachearycells–intheformofnetwork

11. Xylem fibres
▪Deadcells,noprotoplastatmaturity.
▪Sclerenchymatous
▪Long,slender,pointedcellswithgreatlythickenedwallsandfewsmallpits.
▪Cellswithverythicklignifiedsecondarycellwall.
▪Obliteratedcentrallumen.
▪Mainfunction:providesmechanicalsupport.
▪2types;Fibretracheids&Libriformfibres.
▪Longerthantracheids

12. ▪Xylem Parenchyma
▪Livingcomponentofxylem
▪Cellswithcytoplasmandprominentnucleus.
▪Thincellulosiccellwallwithsimplepits.
▪Lignifiedsecondarycellwallabsent.
▪Storestarch,oil,andergasticsubstances.
▪2types;AxialParenchyma&RayParenchyma.

14. SECONDARY XYLEM ONTOGENY & STRUCTURE
▪Secondaryxylemaretypeofxylemproducedduringsecondarygrowthof
angiosperms&somegymnosperm.
▪Thecambiumringcutsoffnewcellsoninnersidearegraduallymodifiedintoxylary
elementscalledsecondaryxylem.
▪Highlyspecialisedvasculartissuescharacterizedbythepresenceofheavilylignified
secondarycellwallcomposedofmainlycellulose,hemicelluloseandlignin.
▪Vascularcambiumcomposesof2typeofstemcells;
(a)fusiforminitials(b)Rayinitials
▪Theelongatedfusiforminitialsdifferentiateintoaxiallyorientedwoodcells(fibres,
vessels,tracheids,axialparenchyma)–ensuringwaterconductionandmechanical
support.
▪Thenearlyisodiametricrayinitialsgiverisetotransverselyorientedray
parenchymaensuringtraverseconductionandnutrientstorage.

15. ▪Thexylemmothercellscutoffbycambiummaydevelopintopermanentxylem
elementswithoutfurtherdivisionormaydivideonceorseveraltimesbeforemature
cellsareformed.
▪Tracheidsareformeddirectlyfromthexylemmothercellbyincreaseinradial
diameterandinlength,thickeningofwallandlossofprotoplast.
▪Woodparenchymacellsareformedbythetransversedivisionofthemothercellintoa
numberofsegmentsandbysubsequentradialenlargementandthickeningofwallsof
thesegments.
▪Theparenchymatousnatureofrayislikelyachievedbyethyleneproducedby
developingtrachearyelements&transportedintherays,inhibitingthedifferenriation
ofnonparenchymatouscellsintheraysandensuringtheirbalanceddistributionin
woodtissue.

16. APOTRACHEAL & PARATRACHEAL PARENCHYMA
1.Apotracheal parenchyma
▪“Trachea,”whichreferstoatubeorpipe(inthiscase,awoodpore).Combinethiswith
theGreekprefix“apo,”whichmeansawayfromorseparate.
▪Apotrachealreferstoparenchymacellsthatoccurseparatefromthepores.
▪Mainlyclassifiedinto3types
▪Apotrachealparenchymacanoccurassinglescatteredcellscalleddiffuseparenchyma.
▪Thesecellsaretoosmalltobeseenwithoutamicroscope.
▪Insomewoodspecies,severalapotrachealparenchymacellsarejoinedoraggregated
together,formingthinbutvisibletangentiallines.Thisformationisknownasdiffuse-in-
aggregatesparenchyma.
▪Whenhorizontal(tangential)bandsofparenchymaoccurasdiffuseinaggregatesknown
asbandedparenchyma.

18. Honduran rosewood (endgrain 10x)

21. 2.Paratracheal parenchyma
▪The counterpart to apotracheal parenchyma is paratracheal parenchyma.
▪The Greek prefix“para” meansbesideornear.
▪Parenchyma that occurs in association with the wood’s pores.
▪It exhibits a much wider range of patterns and variations.
▪Mainly classified into 4 types.
▪The most basic paratracheal parenchyma formation is a ring or circle of
cells surrounding the pore, which is termedvasicentric parenchyma.
▪The words“vase”suggesting a vessel or poreand“centric“,which simply
indicates that the parenchyma is centered around the pore.

22. Acasia

23. ▪Another form of parenchyma that is closely related to vasicentric isAliform
parenchyma whichliterally means“wing-shaped.”
▪There are actually two primary variants of aliform parenchyma: the first
iswinged,where short appendages or wings of parenchyma extend from
one or both sides of the pore.
▪The second variant of aliform islozenge,where the parenchyma
surrounding the pore takes on a diamond or elongated oval shape.
Ramin: aliform-winged
Merbau: aliform-lozenge

25. ▪AnotherformationisConfluentparenchyma.Thisoccurswhentheparenchyma
issoextensivethatitextendsoutwardandmakescontactwiththeparenchyma
fromneighboringpores.
Marblewood: confluent

27. ▪Whenhorizontal(tangential)bandsofparenchymaoccurasextensionsof
aliformorconfluentparenchymaitiscalledbandedparenchyma.
▪Bandedparenchymacanbeincontinuousbands,oritcanoccurininterrupted
ordiscontinuousbands.
▪Thebandscanbeverythickconstitutingoverhalfofthewood’soverallvolume
insomespeciesortheycanbeverythinandhardlyvisiblewithahandlens.
▪Thebandscanbeverynumerousandevenlyspaced,ortheycanbeverysparse
andsporadic.

28. Narra: banded

29. ▪Itconsistofcompactmassofthickwalledcellssoarrangedastoform2systems-
1.Alongtitudinal(vertical)–Axialsystem
2.Atransverseradiatingsystem(runhorizontally)–Raysystem
▪Longtutudinalsystemconsistsofelongate,overlapping&inter-lockedcellsof
tracheids,fibres,vesselelements&alongtitudinalrowofparenchymacells.
▪Itmoveswaterandmineralsupthestem.
▪Secondaryxylemtraversedbyradialsystemofxylemrays(inaradialdirection)
▪Raysystemextendsatrightangletotrachearyelementsandinvolvedinradial
conductionofwaterandmineralsaswellasstorage.
▪Someconiferwoodcontainsresinductsorcanalsinboththeaxial&raysystem.
STRUCTURE

30. ▪Secondaryxylemingeneralconsistofthekindofcellsasthoseofprimaryxylem,
buttypesofvessels,tracheidsfibresareoftenquitedifferent.
▪Vesselsandtracheidsaremostabundantandusuallyshorter,widerandthick
walledthanthatofprimaryxylem
▪Richinxylemfibresthanprimaryxylem.
▪Mostlyvesselsarepitted.
▪Annular&spiraltracheidsandvesselsaltogetherabsent.
▪Xylemparenchymacellsarelongandfusiform,butsometimesshort.Theyare
livingcellsandusuallymeantforstorageoffoodmaterials.
▪Tanninsandcrystalsarefrequentlyfoundinthesecells.
▪Fiberspossessthickwallsandborderedpits.

31. VASCULAR RAYS
▪Astheradialwidthofthesteleincreases,thedistancefromphloemtoxylem
increasesandresultingneedforbetterconductionofwaterradiallyfromxylem
tophloem&cambiumandfoodfromphloemtocambiumandtothelivingwood
parenchymaismetwithbytheproductionofvascularrays.
▪Certaincellsofthecambiumringinsteadofgivingrisetowoodandphloem
elementsproduceparenchymacellswhichformnarrowmedullaryraystraversing
radiallythesecondaryxylem.
▪Theyaresomewhatelongatedandapparentlyfittedforradialconductionoffood
materials.
▪Allvascularraysareinitiatesbycambiumandonceformedareincreasedin
lengthindefinitelybycambium.
▪Commonlycalledmedullaryraysorpithrays.

32. ▪Theseradialraysmaybebestcalledvascularraysastheraysareofvascular
tissuespartlyofxylemandpartlyofphloem.
▪Thepartofvascularraywhichisinthexylemisspokenoffasxylemraysor
woodrays&thatofphloemasphloemrays.
▪Xylemraystraverseinsecondaryxylemandestablishcommunicationwith
livingcellsofvasculartissues.
▪Extendradiallyinsecondaryxylem.
▪Originatefromrayinitials.
▪Xylemraysrunsasacontinuousbandtosecondaryphloemthroughcambium
formingacontinuousconductingsystem.
▪Xylemrayshelpinexchangeofgasesalsoaidinconductionofwaterandfood
fromphloemtothecambiumandxylemparenchyma.

33. FUNCTIONS
▪Conduction of water, nutrients and minerals from root to leaves.
▪Provides mechanical support.
▪Storage of food and other materials.
▪Ray parenchyma forms tyloses which forms ergastic substances.

36. THANK YOU..