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.