Secondary Growth

secondary growth in stems and roots through the vascular cambium

-stem vascular system: vascular cambium cells arise from the residual procambium cells and produce secondary xylem and phloem
-root vascular cambium: first forms as a discontinuous series of sections that eventually form a closed ring

secondary growth in stems and roots through the cork camium

-stem cork cambium: first cork cambium arises from parenchyma cells in cortex; each new cork cambium arises from cortex tissue to the inside until the cortex is used up; subsequent cork cambia arise from the secondary phloem to the inside
-root cork cambium: endodermis and pericycle become inactive; outer layer of enlarged pericycle gives rise to the first cork cambium and forms the periderm

inner bark vs outer bark

-inner bark: living secondary phloem, dead phloem between the vascular cambium and innermost cork cambium, and any remaining cortex
-outer bark: dead tissue (including dead secondary phloem), all layers of the periderm outside of the most recent cork cambium

define bark

all tissues outside the vascular cambium

function of lenticels

-small openings in the outer bark of stems and roots that allows gas exchange

sapwood vs heartwood

-sapwood: consists of the outer xylem rings that still conduct water and minerals
-heartwood: older non-conducting rings of xylem found in the center of the trunk or root

sapwood functions

protects the heartwood from rotting

heartwood functions

used for aging the tree and determining climate conditions

formation of growth rings

growth rings in wood result from yearly growth of xylem rings

potential applications of growth rings in wood

-determining tree age
-interpretation of the climate

reaction wood in dicots and gymnosperms

-tension wood (dicots): forms on the upper side of leaning trunks or branches and pulls (produces wider growth rings, less lignin)
-compression wood (gymnosperms): forms on the underside of trunk or branches and pushes (produces wider growth rings and rich in lignin)