Vegetative morphology- A general account Stems with modifications.

This presentation intends to give the general structure and functions of the stem along with its modifications to address the emerging needs of plants with the passage of time and the ecosystem. It also addresses the anatomical features of the stem. The changes of the stem have been explained with images taken from Google. Some unique features like bulbs, corms, phylloclade, cladode, tuber, runners, creepers, stem branching pattern etc have been highlighted.

1. PLANT
MORPHOLOGY
Vegetative morphology-A
general account stem with
different types of
modifications
By
Dr. N. Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini College, Purulia
Purulia (W.B)
723101, India

2. A GROWING PLANT

3. STEM
•Duringgermination,theplumuleabovethegroundturnintopositively
phototropicandnegativelygeotropicandhydrotropicextendedtoformthe
mainaxisoftheplant;bearsnodesandinternodeswiththeprovisionof
leaves,flowersandfruitsknownasstem.
Derivedfromplumule,
Ascendingaxismostlyaerialorsub-aerialorsometimesunderground,
Positivelyphototropicbutnegativelygeotropicandhydrotropic,
Nodesandinternodespresent,
Nodesderivebranchesandleaves,
Bearsbuds,eitherapicalbudsorreproductivebuds
Branchingextendedexogenously,
Multicellularhairsalmostpresent,Mostlyconjoint,collateralor
bicollateral,endarchvascularbundle,
Diversetypesofmodificationstoaddressthedifferentneedswiththe
passageoftimeandspace.

4. PARTS OF STEM

5. ANATOMY OF STEM
•Thet.softhestemconsistsofthefollowingfeatures:
•Epidermis-uniseriate,parenchymatouswithmulticellularhairsas
epidermaloutgrowth,withcuticularcovering
•Hypodermis-Narrowerparenchymatouscortex,madeupof
collenchymatouscells,
•Stele-Siphonostele,dictyostele,
•Pericycle-multiseriateconsistingofsclerenchymaandparenchyma,
•Vascularbundle-Conjoint,collateralorbi-collateral,openandarranged
moreorlessaring,
•Protoxylemisendarchandphloemoccursontheperipheryoronbothinner
andoutersideofxylem,
•Pithiswelldeveloped,
•Intra-stealersecondarygrowthoccurswiththehelpofcambiumringthatis
partlyprimaryandpartlysecondary,
•Anomalousgrowthofstemveryoftenoccurs.

7. BRANCHING PATTERN
Branchesaresimilarbutsmallercopiesofthemothershoot,
Itarisesfromtheaxilofleaffromaxillariesbud,
Thesebranchesfurtherdeveloplateralbudsonthemwhichdorms
secondaryandtertiarybranches,
Thepatternsinwhichthebranchesartearrangedonthemainaxisare
calledbranching,
Endogenousinorigin,
Thesmallunderdevelopedbranchesaretwigsandthelargerbranches
calledboughs,
Dependingonpattern,itmaybecaudex(unbranchedtrunk),excurrent
(apicalbudsgrowindefinitely)ordeliquescent(growthoflateralbudsare
morethantheapicalbranch),
Itmaybetwotypes-Dichotomous&Lateral.

8. BRANCHING PATTERN

9. BRANCHING PATTERN
•DICHOTOMOUS BRANCHING:
Twobranchesaredevelopedatthegrowingpointofthemainaxis;main
axisbecomefootorpodium,
Theforkedregionagainbecomesbranchedeitherbynormalormonopodial
ortrueandsympodialmanner,
MONOPODIAL-Theapexofthemainaxisbifurcatesandgivesriseto
twodaughteraxesofequalvigor,
Thedaughteraxesfurtherbecomesbranchedlikemainaxis;e.g.
Selaginellamonospora,Lycopodioumclavatum.
•SYMPODIAL-Themainaxisbifurcatesandgivesrisetotwoequally
vigorousdaughteraxes,
Lateronaxisgrowsmorerapidlythantheother,
ItmaybeHelicoidsandScorapoid,
InHELICOID,themainaxistakeplaceinoneside,
InSCORIPOID,themainaxistakesplaceinalternatesides

10. BRANCHING PATTERN
•LATERALBRANCHING
Branchesgrowalwaysfromthesidesofmainaxisduetotheactivityoftheir
lateralaxillarybuds,
Itmaybetwotypes-RacemoseormonopodialorindefiniteandCymoseor
sympodialordefinite.
•RACEMOSE
•Theprimaryaxisgrowsindefinitelyduetotheactivityofterminalbud
thebranchesdevelopedfromtheaxillarybudthatarearrangedinacropetal
succession,
Theterminalbudsremainpersiststhroughoutthelifeoftheplant,
Theplantlookslikepyramidi.e.excurrentinform,
e.g.PolyalthialongifoliaofAnnonaceae,LawsoniaalbaofLythraceae.
•CYMOSE
Thegrowthoftheterminalbudceasesandoneormorelateralbudsdevelop
intobranches,
Theaxillarybudsgrowmorevigorouslythantheterminalone,
Thebranchesbecomesmorethantheprimaryaxis,

11. BRANCHING PATTERN
•Duetocymosetypeofbranching,thetreebecomesdome-shapedi.e.
deliquescentformlikeMangiferaindicaofAnacardiaceae,Ficus
benghalensisofMoraceaeetc.
•Threetypes-Uniparous,BiparousandMultiparous,
•UNIPAROUS-Onebranchdeveloped,maybetwotypes-Helicoidand
Scopiod
•HELICOID-Ifthesuccessivedaughterbranchesdevelopedononeside
only,calledhelicoidasSaracaindicaofCaesalpiniaceae,
•SCORPIOID-Thesuccessivedaughterbranchesdevelopedalternately
fromleftandrightasinVitisquadrangularisofVitaceae.
•BIPAROUS-Twobranchesdevelopedjustbelowtheapicalpointofmain
axis,
•e.gCarissacarundusofApocynaceae,MirabilisjalapaofNyctaginaceae.
•MULTIPAROUS-Morethantwobranchesdevelopedjustbelowtheapical
pointofthemainaxisasfoundinCrotonbonplandianumofEuphorbiaceae

12. BRANCHING AT A GLANCE
•Branching-DichotomousandLateral,
•DICHOTOMOUS-
I.NormalandSympodial
II.SYMPODIAL-HelicoidandScorpoid
•LATERAL-RacemoseorMonopodial,
•CymoseorSympodial
•CYMOSE
I.Uniparous,
II.Biparous,
III.Multiparous
•UNIPAROUS
I.Helicoid,
II.Scorpoid

13. CLASSIFICATION OF STEM
•Stemsarebroadlyclassifiedintotwocategories-ErectandWeekStem
•ERECTSTEM
•Mainlythreetypes-Herbs,ShrubsandTrees
•HERBS-
Ephemeral-Veryshortlifespan,fewdayslikeBalanitesaegyptiaca
Annual-DurationeitheroneseasonoroneyearasOryzasativa,Brassica
napus,
Biennial-DurationeithertwoseasonsormorethanoneyearlikeRaphanus
sativus,Daucuscarota,
Perennial-MorethantwoseasonsortwoyearslikeZingiberofficinale,
Cannaindica
•SHRUBS
•Woody,shortstemwithnumerousbranchinghavingbushyappearancelike
Hibiscusrosa-sinensis,Gardeniafloridaetc.

14. CLASSIFICATION OF STEM

15. CLASSIFICATION OF STEM
•TREES:
•PERENNIAL,Tall,solidwiththicktrunkgenerallytreatedastreeswiththe
followingtypes-
Caudexes-Tall,unbranchedlikeCocosnucifera(Arecaceae)
Excurrent-Growindefinitelyandbranchesofthelateralsidesappearlike
crownasfoundinPolyalthialongifolia,
Deliquescent-Duetothedefinitebranchingfromthelateralpartsappear
likepyramidasfoundinFicusbenghalensis,
Culm-Mostlyinmonocotyledons,thenodeissolidandtheinternodes
hollowasfoundinBambusaarundinaceainPoaceae.
•Scape:Ascapeisapedunclearisingfromasubterraneanorvery
compressedstem,withthelowerinternodesverylongandhencefeworno
bracts.Afteracertainseason,theundergroundstemsanerectshootappear
andproduceinflorescencelikestructureasPolyalthiatuberosa,Allium
cepa

16. Polyalthia sp.

17. CLASSIFICATION OF STEM
•WEAK STEMS
•Soft stem, can not remain erect, comprises of three types as follows:
•Creepers-Creepers,asthenamesuggests,areplantsthatcreeponthe
ground.Theyhaveveryfragile,long,thinstemsthatcanneitherstanderect
norsupportalltheirweigh,adventitiousrootsderivefromthenode
Examplesincludewatermelon,strawberryFrageriasp),pumpkin
(Cucurbitamaxima)andsweetpotatoes(Ipomeabatatus,
Convolvulaceae).
•Trailers-plantsthatcreepontheground.Theyhaveveryfragile,long,thin
stemsthatcanneitherstanderectnorsupportalltheirweigh,adventitious
rootsnotderivefromthenodeasfoundbroadlyoftwotypes-
•Procumbent-TheupperpartgrowprostratelikeBasellarubra,
•Decumbent-TheupperpartstandserectlikeLindenbergiautricaefolia
(Orobanchaceae).
•Climbers-Plantswithweakstemsthatcannotstanduprightandspread
readilyonthegroundandcreepsalongwiththerootortendrilupwards.
Consistsoftwotypes-

18. CLASSIFICATION OF STEM
StemClimbers-Climbwiththesupportfromstemorthetendrilasfoundin
Dolichoslablab,Clitoriaternatea,;whenitclimbsfromlefttorightcalled
dextroseasinDolichossp.andfromlighttoleftiscalledSinistroseasin
Clitorea.
Tendrilclimbers-Whentheclimbersgrowwiththetendrilasfoundin
Pisumsativum,Passifloraedulisknownastendrilclimbers.
RootClimbers-Whentheweakstemsclimbswiththehelpofadventitious
rootsderivedfromthenodeasfoundinPiperbetle,Aciedapsusofficinalis.
HookClimbers-Whentheplantsclimbwiththehooksderivedfromany
partofthestemasfoundinArtabotrysodoratissmusetc,
ThornClimbers-Whentheclimbersclimbwiththehelpofthornsasfound
inCalamusrotang,Bougainvilleaspectabilisetc.
Branchingofthestemsmaybetwotypes-Dichotomousandlateral,lower
pantshavedichotomousbranchingbuttheangiospermsenjoylateral
branching.

19. STEMS DIVERSITY-AT A GLANCE
•STEM-Aerial, Modified, Metamorphosed
•AERIAL-Strong & Weak
•STRONG
Excurrent e.g. Pinus sp.
Deliquescent, e.g. Magnolia indica
Caudex e.g. Cocos nucifera,
Culm, e.g. Bambusa tulda
•WEAK
•Trailer, Creeper, Climber
•TRAILER-
Procumbent, e.g. Basellaa rubra, Decumbent, e.g. Tridax procumbens,
•CREEPER
Twiner, e.g. Dolichos lablab,
Tendril climber, e.g. Vitis vinifera

20. Magnolia grandiflora

21. STEMS DIVERSITY-AT A GLANCE
Root Climber, e.g. Piper betel,
Scrambler, e.g. Zizyphus jujuba,
Hook Climber, e.g. Bignonia sp.
Adhesive Climber, e.g. Ficus repens,
Lianas, e.g. Hiptage madabola.
•MODIFIED
•Sub aerial & Underground
•Sub aerial
Runner, e.g. Centella asiatica
Stolon, e.g. Mentha piperita,
Offset e.g. Eichhornia crassipus,
Sucker, e.g. Mentha viridis.
Underground Rhizome, e.g. Zingiber officinale,
Tuber, e.g. Solanum tuberosum

22. STEMS DIVERSITY-AT A GLANCE
•Corm, e.g. Cocos sativus
•Bulb-Tunicated, e.g. Allium cepa; Scaly, e.g. Lilium candidum
•METAMORPHOSED
Thorn, e.g. Aegle marmelos,
Stem tendril, e.g. Passiflora suberosa,
Cladode, e.g. Asparagus racemosus,
Pseudo bulb, e.g. Orchid,
Bulbils, e.g. Globba bulbifera

23. BUDS & TYPES OF BUDS
•Small,unfurledandcondensed,immatureshootistreatedasbud.
•KINDSOFBUDS
•Accordingtonature-
•Vegetativebud-Givesstemandbranches
Floralbud-produceflower,
Tendrillarbud-ThebudstransformedintotendrilasfoundinPassiflorasp.
ACCORDINGTOORIGINANDPOSITION
Apicalbuds-Foundtooccurinapexandtipofthebranches,
Accessorybuds-Thenodeoftheleavescompriseanumberofbudsas
foundinbringel,Chiliesetc,
Dormantbuds-Theapicalbuddoesnotdevelopbranchingandremain
dormant.
ADVENTITIOUSBUDS
Whenthebudsderivenotfromitsdesiredlocationbutelsewherecalled
adventitiousbudsasfollows:

24. BUDS

25. BUDS & TYPES OF BUDS
•Epiphylousbuds:ThebudsderivedfromtheleafasfoundinBigoniasp.
•Caulinebuds-Whenthebudsderivedfromthedecapitatedportionofstem
orbrancheslikeRose,Dahlia,Durantaetc.
•Radicalbuds-Thebudsderivedfromtheundergroundmodifiedrootlike
Trichosanthusdioica,Sweetpotatoetc,
•Budscale-thebudsveryoftencoveredbyscalybractsandthesecan
transformbudsasfoundinJackfruit,Micheliachampkaetc.
•Winterbuds-Thelowtemperaturedefoliatetheleavesbutthebuds
developedinthestemundergoesrestinganddormancy,laterongiverise
totheleavesasfoundincauliflower,cabbageetc.
•Bulbils-Theaxillarybudsmayswellduetostorageoffood,appear
circularcalledbulbilsasfoundinDioscoreabulbifera

26. FUNCTIONS OF STEM
Tobearbranches,flowers,fruitsseed,
Helpintransportationofwaterandmineralsandtranslocationof
synthesizedfood,
Todevelopnewcells,tissuesandorganstoaddresstheemergingneed,
Foodstoragelikepotato,zingeretcasundergroundstem,
Tostorewaterlikecactusandotherxerophytes,
Toperformphotosynthesislikecactus,
Tohelpinclimbingbyhooks,tendril,spinesetclikePassiflora,
ToextendprotectionbythemodificationofaxillariesbudslikeLemon,
Duranta,elephantappleetc,
Toexpeditevegetativepropagationlikepotato,china-roseetcToconfer
perennationlikeZinger,Cuminetc,
Toreducetranspirationbymodofiedstemslikephyllode,phyllocladeor
spinesasinAcacia,Cactusetc,
Toextendsexualreproductionbytheflowerandotheragents.

27. MODIFICATION OF STEM
•Toextendthesecondaryfunctionsofstemlikefoodstorage,protection,
reproductionandtowithstandadversecircumstances,thestemundergoes
modificationbythedifferentwaysasstatedbelow:
Undergroundmodifiedstem,
Sub-aerialmodifiedstem,
Aerialmodifiedstem.
•UNDERGROUND MODIFIEDSTEM
•Itconsistsofnodesandinternodes,axillariesbudsandscaleleaves.
•TUBER-
Fleshyundergroundbranchorpartofit,
Developintheaxilofleafonthemainstem,
Apexofthebranchesswellupduetoaccumulationoffoodeitherround,oval
orelongatedshapewithmultiplenodesandinternodes,
Eyesaresituatedonthedepressions,
Axillarybudsdevelopnewshootwithadventitiousrootsatthebaseofthe
stem.
E.g.SolanumtuberosumofSolanaceae,CyperusrotundusinCyperaceae

28. MODIFICATION OF STEM

29. MODIFICATION OF STEM
•RHIZOME
Elongated,thickdorsiventralstemwithnodesandinternodes,
Eachnodebearsbrownishscaleleaveshavingbudinitsaxil,
Someaxillariesbudsdevelopaerialshootannually,
Largenumberofadventitiousrootsdevelopfromthelowersideoftherhizome,
Aterminal;budispresentintheandtheolderportiongraduallydie,
Whentherhizomegrowsverticallyinsteadofhorizontallycalledrootstock,
MusaparadisiacaofMusaceae,AlocasiaindicaofAraceae,Nymphaea
stellataofNymphaceae.
CORM
Morelessround,solid,stoutandverticallyfleshyundergroundstem,
Developatthenodesofaxilsofthin,membranousscaleleaves,
Adventitiousrootsdevelopfromthebaseofalloveritsbody,Apicalbudis
comparativelylargerinsize,
AmorphophalluscampanulatusandColocasiasp.OfAraceae,Crocussativus
ofLiliaceae

30. SAFFRON,Crocus sativus

31. MODIFICATION OF STEM
•BULB
Modified,undergroundstemlookslikebud,
Stemisextremelyreducedtoashortandconvexdiscwithcompressed
internodes,
Leavesdevelopedfromtheuppersurfaceofthestem,
leafbasesarethick,fleshyandarrangedconcentrically,
Terminalbudpresentontheupperregionofthestem,
Axillarybudspresentintheaxiloftheleaves,
Maybetwotypes-TunicatedorCoatedAndScalyornaked
TUNICATED-Thefleshyleafbasesarrangedregularlyandenclosedina
concentricmanner,
TheouteronebecomesdryandscalythatformstunicaasAlliumcepaof
Liliaceae.
•SCALY-Fleshyleavesareoverlapped,notcoveredwithtunicaasTulipa
gesnerianaofLiliaceae

32. Tulipasp.

33. METAMORPHOSED STEM
Here,thestemshowsextrememodificationandbecomesdifficulttofindits
originalmorphologicalnature,
Theanatomycanconfirmthemorphology,
Itistreatedasmetamorphosedstem,
Maybeoffollowingtypes
•THORN OR STEM SPINE
Axillary branches growth arrested and metamorphose into hard and sharply
pointed structure, the thorns,
Acts as defensive organ being sub-epidermal in origin,
DurantaplumieriofVerbenaceae,HygrophlaauriculataofAcanthaceae,
AeglemarmelosofRutaceae,Prunussp.,ofRosaceae,Carissacarundasof
Apocynaceae,FlacourtiacataphractaofFlacourtiaceaeetcastheydevelop
intheaxilofleaves,oftenbearfoliageandlateralbrancheswithstemlike
internalarchitecture.

34. Durant erecta

35. METAMORPHOSED STEM
•STEM-TENDRIL
Stemmetamorphosedintoaslenderandcoiledstructuretoclimbasin
PassifloasuberosaofPassifloraceae,
Tendrilsdevelopintheaxilofleaf,
InVitisquadrangularisofVitaceae,theterminalbudbecomesmodified
intoatendril,
Fromtheaxiloftheleaf,anotherbranchdevelopswhoseapexsimilarly
becomesmodifiedintotendrilofsympodialtype.
PHYLLOCLADE ORCLADOPHYLL
Flatlikemetamorphosedstemconsistingofmanynodesandinternodesand
functionsasleaf,
Theleavesmayeitherfallofforbecomeverysmallormodifiedinto
spines,
Itreducetranspirationrateandactsaswaterstorageorgan,
Pricklypear,OpuntiadilleniiofCactaceae

36. Passiflorasp.

37. METAMORPHOSED STEM
•CLADODES
Themetamorphosedleaflikebranchesconsistingofoneinternodesare
calledcladode,
Developintheaxilofminutescaleleave4s,
Servethefunctionoffoliageleavesforphotosynthesis,
AsparagusracemosusofLiliaceae.
PSEUDOBULBS
Itismodifiedstemconsistsofoneinternode,
Becomesfleshyandtuberousstructure,
Storeexcessmoistureandwithunfavorablecondition,
FoundinaerialOrchids.
BULBILS
Itisakindofmodifiedbudandplaystheroleofreproductionasstated
earlier.

38. Opuntiasp.

39. THANKS FOR YOUR VISIT
•REFERENCES:
1.DifferentWebPagesforstudymaterialsandcontent,
2.Googleforimagesforbetterillustrations,
3.ATextbookofBotany,Vol.II-Bhattacharya,Hait,Ghosh
•Disclaimer:
•Thispresentationhasbeendevelopedtoenrichtheonlinefreestudy
materialsforacademicfraternitywithoutanyfinancialinterests.The
presenteralwaystakesthepleasureofhappinesstoreachtheunreached.

40. “There's no better feeling than making your little
girls laugh.”