StemsStems3 Functions:3 Functions:

Support leaves Support leaves and reproductive and reproductive structuresstructures

Internal transportInternal transport

Produce new Produce new tissuetissue

External StucturesExternal Stuctures

Internal Structures: Internal Structures: MonocotsMonocots

Most herbaceousMost herbaceous Exception: PalmsException: Palms

Vascular bundles Vascular bundles

Ground tissueGround tissue

No lateral No lateral meristemsmeristems

Internal Structures: Internal Structures: Herbaceous DicotsHerbaceous Dicots

CortexCortex

Vascular tissueVascular tissue Some have Some have

vascular vascular cambiumcambium

Annual vs. Annual vs. PerrenialPerrenial

PithPith

Woody Stems of EudicotsWoody Stems of Eudicots

Primary tissue arranged like that in Primary tissue arranged like that in herbaceous stemherbaceous stem

Secondary growth Secondary growth GirthGirth Vascular cambiumVascular cambium Cork cambiumCork cambium

Once secondary growth begins, internal Once secondary growth begins, internal structure changes structure changes

Secondary GrowthSecondary Growth

Vascular cambium Vascular cambium become continuousbecome continuous

Cells in cambium Cells in cambium produce daughter cells produce daughter cells in 2 directionsin 2 directions

After division, 1 cell After division, 1 cell remains meristematicremains meristematic

As secondary tissue forms 1As secondary tissue forms 1o o xylem and xylem and phloem become separated from each phloem become separated from each otherother

11oo tissue outside cylinder of growth tissue outside cylinder of growth crushed or torn apartcrushed or torn apart

22oo xylem and phloem contain same types xylem and phloem contain same types of cells and perform same function as of cells and perform same function as primary tissueprimary tissue

Rays connect 2Rays connect 2oo xylem and phloem and xylem and phloem and allow for lateral transport of materialallow for lateral transport of material

Cork CambiumCork Cambium

Arises from parenchyma cells in outer Arises from parenchyma cells in outer cortexcortex

Produces peridermProduces periderm

Cork cells form to the outsideCork cells form to the outside Dead at maturityDead at maturity Waterproof & Impermeable to gasesWaterproof & Impermeable to gases

Cork parechyma form to insideCork parechyma form to inside

Common Wood TermsCommon Wood Terms SoftwoodSoftwood

HardwoodHardwood

Sapwood Sapwood

Heartwood – Older wood, in centerHeartwood – Older wood, in center

Annual RingsAnnual Rings

Used to determine the age of a tree Used to determine the age of a tree in temperate climatein temperate climate

Difference between springwood and Difference between springwood and summerwoodsummerwood Springwood – large diameter of Springwood – large diameter of

conducting cells, few fibersconducting cells, few fibers Summerwood – narrower conducting Summerwood – narrower conducting

cells, more fiberscells, more fibers