BIOL 2P93 Lecture 22: 22. The Gymnosperms LC pt 1
24 Jan 2016
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Section of vascular bundle: phloem occurs in interior + exterior to xylem. Vascular cambium develops btwn secondary phloem + xylem, not btwn primary phloem + xylem. Vascular cambium made secondary phloem external to outside + some secondary xylem inside. When wood laid down in spring: secondary xylem cells have large diameters, lighter in color, thin-walled + wide apart from each other indicates there is a lot of available water = spring xylem further spring (early wood). Figure below: indication of early + late wood of a conifer w/ annual rings. Cork cambium (phellogen): another type of cambium/lateral meristem gives to secondary growth. Responsible for forming periderm (outer protective layer of plant that replaces epidermis destroyed during secondary growth). Periderm has a cork, cork cambium + phelloderm. Cork (phellem)/outer portion of periderm: non-living cells at maturity w/ suberized cell walls resists passage of gases + water vapor. Phelloderm: tissue of periderm formed inward + opposite to cork, inner portion of periderm.
