Stem

FUNCTIONS  1.Conductionoffoodandwater  2.Formationandsupportofleavesandbuds  3.Storageoffood

ORIGINOFSTEMS  Epicotylistheembryonicoriginofstems  Plumuleisthefirstbud  The2termsare

sometimesusedsynanymously

EXTERNALSTRUCTUREOFSTEMS  Nodes  Internodes  Leaves  Buds  Leafscar  Vascularbundlescar  Budscales  Budscalescar  Lenticels

Primarygrowthoftheplantbody

Procambium

Ground meristem

Protoderm

PRIMARYPERMANENTTISSUES

PRIMARYPERMANENTTISSUES  1.Epidermis  2.Cortex  3.Vasculartissues  4.Pith

  5.Endodermis  6.Pericycle

  3.Vasculartissues A.Primaryxylem

 Protoxylem– Firstpartofthe10xylemtomature Madeupoftrachearyelementsandparenchyma

 Metaxylem‐ Laterpartofthe10xylemtomature Withtrachearyelements,parenchymaandfibers

Primaryxylemdevelopment

  EXARCH–Firstxylemelementstomaturearefarthestfromthecenteroftheaxis;maturationincentripetaldirection

  ENDARCH‐Theinitialelementsoccurnearest,

andthelatestfarthest,fromthecenteroftheaxis;maturationiscentrifugal

  3.MESARCH–Differentiationprogressesin2ormoredirectionsfromthefirstmaturexylemelements

PrimaryxylemdevelopmentLefttoright‐A.Lycopodiumflabelliformerhizome;B.Osmunda;C.Quercusstem

B.PRIMARYPHLOEM

  PROTOPHLOEM‐Withsieveelements,mayhavenocompanioncells;functionforashortperiodoftime,destroyedinrapidlyelongatingorgans

  METAPHLOEM‐Withsieveelements,companioncellsandparenchyma;indicotsfibersareabsent

  CENTRIPETALDIRECTIONofdifferentiation  CENTRIFUGALDIRECTIONofdifferentiation

PrimaryphloeminZeamays

VascularbundleofRanunculus

Ricinushypocotyl

VascularbundleinCucurbitamaxima

VASCULARBUNDLES‐Strandsofconductingtissue

TYPES:  A.COLLATERALBUNDLE‐Abundlewith

phloemononesideofxylemonly,commonlyexternaltoit  1.CLOSED–Withoutvascularcambium  2.OPEN‐Withvascularcambium

  B.BICOLLATERALBUNDLE‐Abundlewithphloemonbothsidesofthexylem

VASCULARBUNDLES

TYPES:  C.CONCENTRICBUNDLES–Abundlewhere

onevasculartissuesurroundstheother

  1.AMPHIVASAL‐Abundlewherethexylemsurroundsthephloem

  2.AMPHICRIBRAL–Abundlewherethephloemsurroundsthexylem

Typesofbundle

Typesofbundle

PRIMARYPERMANENTTISSUES  1.Epidermis  2.Cortex  3.Vasculartissues  4.Pith

  5.Endodermis  6.Pericycle

  4.PITH

  5.ENDODERMIS‐theinnermostlayerofthecortex

  6.PERICYCLE‐thefundamentaltissueofthestele;thefundamentaltissuebetweentheendodermisandthevascularcylinder

  STELE‐madeupofthevascularsystemandconjunctivetissue(interfascicularregions,thegaps,thepith,ifpresent)andthepericycle

StarchsheathinRicinus

PerivascularfibersinCucurbita

TYPESOFSTELE

  PROTOSTELE‐Solidcolumnofvasculartissuewithoutpith

  A.HAPLOSTELE–solidcoreofxylemsurroundedbythephloeme.g.,Selaginella

  B.ACTINOSTELE‐thexylemtissueisstar‐shapedandsurroundedbythephloeme.g.Psilotum

  C.PLECTOSTELE‐thexylemstrandsareinlongitudinalfilesorinaplatelikearrangementandthephloemtissuesareinterspersedwiththexylemtissuese.g.Lycopodium

 TYPESOFSTELE

  SIPHONOSTELE‐vasculartissuesurroundsanon‐vascularcore,thepith

  A.ECTOPHLOICSIPHONOSTELE‐thephloemoccursoutsidethexylemcylinder

  B.AMPHIPHLOICSIPHONOSTELE(SOLENOSTELE)‐thephloemdifferentiatesoutsideandinsidethexylemcylinder

  DICTYOSTELE‐asiphonosteleinwhichlargegapsarelargesothatsteleisdividedintoseparatebundles

  EUSTELE‐astelewithinterfascicularparenchymaandcollateralorbicollateralbundles

  ATACTOSTELE‐astelewithscatteredbundles

NODESANDINTERNODES(ANATOMY)

  1.Differinarrangementofvasculartissues

  A.LEAFTRACE‐avascularbundlelocatedinthestembutdirectlyrelatedtotheleaf

  B. LEAFGAPORLACUNAE‐theparenchymaregionlocatedadaxiallyfromthedivergingleaftrace

Leaftraceandgap

  TYPESOFNODE  1.ONE‐TRACEUNILACULAR‐withasinglegapandasingletracetoaleaf

  2.TWO‐TRACEUNILACULAR‐with2tracesandasinglegaptoaleaf

  3.TRILACUNAR‐with3tracesand3gapstoaleaf(1medianand2lateral)

  4.MULTILACUNAR‐withseveraltomanygapsandtracestoaleaf

NODESANDINTERNODES(ANATOMY)

Typesofnode

Typesofnode

NODESANDINTERNODES(ANATOMY)

  1.Differinarrangementofvasculartissues

  C.BRANCHTRACES‐vascularsupplyofthebranchlocatedonthestem

 D.BRANCHGAP‐theparenchymaregioninthevascularcylinderabovethepositionwherethebranchtraceentersthebranch

  2.Thecortical andpithcells maybeshorter inthenodesandtheremaybelesssclerenchymaandmorecollenchyma

  3.Ifthepithisdestroyedduringthegrowthofthestem,  thenoderetainsthepith(nodaldiaphragm)whiletheinternodeishollow

  orseriesofhorizontalplatesofpithareleft(diaphragmedpith)

NODESANDINTERNODES(ANATOMY)

Cucurbitastem

PRIMARYGROWTHOFTHEAXIS

  INCREASEINHEIGHT  primarilythroughgrowthofinternodesby:

  INCREASEINDIAMETER  ASARESULTOF: diffusegrowth  celldivisionrestrictedtocortexandpith celldivisionrestrictedtoprimarythickeningmeristem

Primarythickeningmeristem

Secondarygrowthoftheplantbody

VASCULARCAMBIUM  forms20vasculartissues  arehighlyvacuolated  withprimarypitfields

 CELLTYPES  FUSIFORMINITIALS‐elongatedwithtaperingends

  RAYINITIALS–nearlyisodiametric,relativelysmallcells

 ARRANGEMENTINTRANSECTION  arrangedinradialseries‐cellsofthecambialzone(initialsandimmediatederivatives)

 ARRANGEMENTINTANGENTIALVIEWS  1.STORIEDORSTRATIFIEDCAMBIUM–fusiforminitialsinhorizontaltierswiththeendsofcellsappearingatexactlythesamelevel

  2.NONSTORIEDORNONSTRATIFIEDCAMBIUM‐thefusiforminitialsarenotinhorizontaltiers;theirendsoverlap(moreprimitive)

Vascularcambiumintangentialsection

 CELLDIVISION

 1.MULTIPLICATIVEDIVISIONS–radial(anticlinal)divisionsthatincreasethenumberofinitials

 2.ADDITIVEDIVISIONS–tangential(periclinal)divisionsthatcontributecellstothesecondaryxylemandsecondaryphloem

Multiplicativedivisionsinfusiforminitials

 DEVELOPMENTALCHANGES Newraysmayarisefromfusiforminitialsortheirsegments 1.fromtheapexoffusiforminitial 2.fromthesideoffusiforminitial 3.bytransversedivisionsofafusiforminitial

  INCREASEINWIDTHANDHEIGHTOFRAYSMAYRESULTFROM:  1.radialdivisionsofarayinitial  2.fusionof2ormoregroupsofrayinitials(bychangesintheinterveningfusiforminitials(lossofsome,divisionandconversiontorayofothers)

Originofraysfromfusiforminitials

Increaseinwidthofray

Increaseinheightofray

Increaseinheightofray

 SPLITTINGOFRAYS  1.throughintrusivegrowthoffusiforminitialsfromagroupofrayinitials

  2.throughelongationofrayinitialsintofusiforminitialsislesscommon

 LOSSOFINITIALS  1.FUSIFORMINITIALS A.conversiontorayinitials

 B.maturationinto20xylemor20phloemelements

Splittingofrays

 LOSSOFINITIAL  2.RAYINITIALS A.maturationinto20xylemor20phloemelements

STORIEDANDNONSTORIEDWOODS

  1)NONSTORIEDCAMBIUM‐formsnonstoriedwood

  2)STORIEDCAMBIUM–formsstoriedornonstoriedwood

GROWTHRINGS/ANNUALRINGS

  EARLYWOOD(SPRINGWOOD)–lessdense,largercellsandsmalleramountofwallsubstance

  LATEWOOD(SUMMERWOOD)–smallercellswiththickerwalls

Vascularcambiumintangentialsection

Earlywoodandlatewood

Earlywoodandlatewood

SAPWOOD/HEARTWOOD

  SAPWOOD‐functionalpartofthe20xylem

  HEARTWOOD–non‐functionalpartofthe20xylem

SECONDARYVASCULARTISSUES

  AXIALSYSTEM–originatesfromfusiforminitials

  RAYSYSTEM–originatesfromrayinitials

GYMNOSPERMWOOD  AXIALSYSTEM

  tracheids  fiber‐tracheids  axialparenchyma

  RAYSYSTEM maybecomposedofrayparenchymaonlyorwithraytracheids

 rayparenchyma raytracheids‐withborderedpitsandlackofprotoplast;withlignifiedwalls;occuratthemarginsofray

Thegymnospermwood

Pinewoodincrosssection

  HOMOCELLULARRAY  HETEROCELLULARRAY

  resinducts‐inaxialsystemorbothaxialsystemandraysystem

Pinewood

ANGIOSPERMWOOD

  morecomplexthangymnospermwood

DISTRIBUTIONOFVESSELS

  1. DIFFUSE POROUS‐ essentially equaldiameters of vessels and uniformly distributedthroughagrowthring

  2. RING POROUS – with vessels of unequaldiameters;withthelargestvesselslocalizedinearlywood

Angiospermwood

SecondaryxylemofPopulusdeltoides

WoodofQuercusalba

DISTRIBUTIONOFAXIALPARENCHYMA

  1.APOTRACHEALTYPE‐thepositionofparenchymaisindependentofthatofvessels

  A.DIFFUSE–dispersedthroughoutthe growthring

  B.BANDED–appearinbands

  C.MARGINAL–limitedtotheperiphery

  1)INITIALPARENCHYMA–restrictedtothebeginningofaseasonalincrement

 2)TERMINALPARENCHYMA‐restrictedtotheendofaseasonalincrement

PortionoftheWoodofQuercusalba

Apotrachealbanded

SecondaryxylemofZygophyllumdumosum

  2.PARATRACHEALTYPE‐thetwokindsofelementsareassociatedwithoneanother

  A.SCANTY‐occasionalparenchymacellsassociatedwiththevessels

  B.VASICENTRIC‐surroundingthevessel

  C.ALIFORM–vasicentricwithwing‐liketangentialextensions

 D.CONFLUENT – coalesced aliform withformingirregulartangentialordiagonalbands

scanty vasicentric

STRUCTUREOFRAY

  withrayparenchymaonly

  HOMOCELLULARRAY–ifitcontainsonlyprocumbentoruprightray

  HETEROCELLULARRAY–ifitcontainsbothtypesmorphologically

RAYSYSTEM

  HOMOGENEOUSRAY–raysareallhomocellular

  HETEROGENEOUSRAY–raysareallheterocellularorsomearehomocellular,othersheterocellular

SECONDARYGROWTHINMONOCOTYLEDONS  theactivityofthismeristemresemblesthat

concernedwiththeprimarythickeninginsomemonocots

  thesemeristemsmaybedevelopmentallycontinuousiffoundinthesameplant

TYPESOF20GROWTHINMONOCOTS

  diffuse20growththroughdivisionandenlargementofgroundparenchyma(e.g.palms)

  20growthfromarestrictedmeristem(cambium)formedinthecortexoutsidethevascularbundles(herbaceousandwoodyLilifloraee.g.Aloe,Sansevieria,Yucca,Agave,Dracaena)

Primarythickeningmeristem

SECONDARYGROWTHINMONOCOTYLEDONS

COMMONFORMSOF20GROWTH

  1. The 10 vascular tissues form an almostcontinuous vascular cylinder and the 20vasculartissuesdothesame

  2. The10 vascular tissues forma systemofstrands,butthe20vasculartissuesariseasacontinuousring

YoungstemofTilia

OldstemofTilia

ANOMALOUS20GROWTH  Deviatingmethodsof20thickening  Lesscommongrowthpatternsamongplants

investigatedthusfar