Section 10: Secondary Growth

Secondary growth

-inc in thickness

-caused by lateral meristems

-plants that live mult yrs will perform primary + secondary growth simultaneously depending on tissue/region of plant

Vascular cambium

-arises from procambium (meristem) in between 1⁰ phloem and 1⁰ xylem—both created by procambium

-will produce 2⁰ phloem (to outside) and xylem (to inside), pushing 1 xylem inward and phloem outward

-more 2⁰ xylem created usually

Cork cambium

-meristematic cell layer that create cork (to outside) and phelloderm (to inside)

-created by dedifferentiation of epidermis, ground cells, or phloem cells

Periderm

-cork cambium, cork, and phelloderm

-replaces epidermis which dies/falls off

Cork cells

-contain lots of suberin, wax, and lignin and will die at maturity

Bark

-all tissues outside of vascular cambium

-1⁰ and 2⁰ phloem, cortex, phelloderm, cork cambium, cork epidermis

-after first yr of growth, new periderm may appear within 2⁰ phloem, pushing more phloem layers into bark

Wood

-2⁰ xylem

-most important plant tissue to humans

-shelter, weapons, etc

Wood features: Resin ducts

-spaces between the xylem cells, lined w parenchyma that produce resin

-ducts created in response to damage

-conifer only

-resin can prevent infection

Wood features: growth rings

-seasonal growth-production of 2⁰ xylem and phloem

-phloem growth may not be obvious bc it gets smashed w other bark tissues

-enviro conditions control width of annual ring

-rings can indicate temp, rainfall, age

Late vs early wood

late: very dense (thinner) and tightly packed

early: less dense, wider

Heartwood

-oil, resins, etc cause wood to darken

Sapwood

-still living xylem cells

Knots in wood

-as tree ages/grows, branches that were lower on the stem die and remains of branches are engulfed by expanding wood layers