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22.2Roots,Stems,andLeavesRoots
§ Therootisusuallythefirststructuretogrowoutoftheseedwhenitsprouts.
§ RootstakeinwaterRootStructureandGrowth
§ Thetipofarootiscoveredbytherootcap.§ Thelayerbelowtheepidermallayeristhecortex.§ Thelayerofcellsattheinnerboundaryofthecortexistheendodermis.§ EncirclingeachcelloftheendodermisisawaterproofstripcalledaCasparianstrip.§ Thelayerofcellsdirectlynexttotheendodermistowardthecenteroftherootiscalled
thepericycle.
TypesofRoots§ Taprootsystem
§ Consistsofathickrootwithafewsmaller,lateral-branchingroots§ Fibrousrootsystem
§ Numerousbranchingrootsthatareaboutthesamesizeandgrowfromacentralpoint
§ Modifiedroots§ Pneumatophores§ Adventitiousroots
StemStructureandFunction§ Themainfunctionofaplant’sstemissupportofa
plant’sleavesandreproductivestructures.§ Transportwateranddissolvedsubstances§ Storesfoodandwater
LeafStructure§ Aflattenedsurfacecalledabladehasalargesurfaceareaforphotosynthesis.§ Theblademaybeattachedtothestembyapetiole.§ Mostleaveshavethesameinternalstructure.§ Theinternalstructureofmostleavesiswell-adaptedforphotosynthesis.§ Tightlypackedcellsdirectlybelowaleaf’supperepidermiscontainmanychloroplasts
andmakeupthetissuecalledthepalisademesophyll.§ Belowthepalisademesophyllisthespongymesophyll.
GasExchangeandTranspiration
§ Theepidermisoftheleafhasmanyporesthroughwhichgasesmayenterorleave.§ Waterevaporatesfromtheinsideofaleaftotheoutsidethroughastomatainaprocess
calledtranspirationthathelpspullthewatercolumnupward.