Biol 3080 Friday 4/1 notes
Biol 3080 Friday 4/1 notes BIOL 3040
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This 4 page Class Notes was uploaded by Casey Notetaker on Thursday March 24, 2016. The Class Notes belongs to BIOL 3040 at Clemson University taught by Christina Wells in Spring 2016. Since its upload, it has received 13 views. For similar materials see Biology of Plants in Biology at Clemson University.
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Date Created: 03/24/16
Friday 4/1- Wood: Secondary Xylem 1. Last time: a. Life cycles: annual, biennial, and perennial b. Perennial plants can be herbaceous perennials or woody perennials c. The vascular cambium i. Ray Initials: cells in the VC that give rise to the wood rays ii. Fusiform initials: vertically elongated cells in the VC that give rise to secondary xylem and phloem iii. *Secondary xylem and phloem are produced by periclinal divisions of vascular cambium d. The cork cambium and periderm i. Periderm formation follows the initiation of secondary xylem and phloem ii. First periderm usually arises from a cortical cell layer just beneath the epidermis iii. Periderm replaces the epidermis as the protective covering on woody stems and roots 1. Refers to the cork cambium and the two things that it makes: cork and phelloderm iv. As it develops, the periderm ruptures the epidermis v. The cork cells are dead when functional, their inner walls lined with wax and suberin waterproof vi. The phelloderm cells are less numerous and resemble cortical parenchyma e. Lenticels: allow gas exchange through the periderm i. The surface of the outer bark of many species is perforated by corky lenticels ii. Commonly arise beneath stomata in the epidermis just prior to the formation of the first periderm 2. How do the outer tissues keep pace with the growing xylem core? a. Anticlinal divisions in VC b. Dilation of phoem rays c. Formation of new periderms d. Some terms: i. Bark: all tissues external to the VC; includes secondary phloem and one or more periderms ii. Inner bark: secondary phloem iii. Outer bark: one or more periderms; 1. Outer bark appearance is influenced by the locations o the sequent cork cambia and by how their derivatives develop these anatomical characteristics determine bark texture 2. This bark structure depends on the relative abundances of its constituent tissues but generally contains collapsed and otherwise non-conducting secondary phloem that has become isolated by cell divisions in the cork cambium iv. Phellogen: cork cambium; these two terms mean the same thing v. Periderm: phelloderm + cork cambium + cork 3. Wood a. Conifer wood i. Simpler in structure than angiosperm wood; only tracheids, no vessels ii. Axial system is almost entirely tracheids iii. The very few axial parenchyma cells are associated with resin ducts 1. Intercellular spaces lined with thin-walled parenchyma cells that synthesize and exude resin 2. Resin: a viscous liquid, composed mainly of volatile fluid terpenes with additional non- volatile solids which make it thick and sticky a. Functions as both chemical and physical defense b. Constitutive and induced (“traumatic resin canals”) c. May be under positive pressure in canals iv. Tracheids have bordered pits through which water passes and which can close in the event of an air embolism v. Radial system consists of relatively small wood rays with resin ducts b. Angiosperm Wood i. The top of angiosperm wood section is more complex: large diameter vessels and small diameter vessels/tracheids, large wood rays, fibers ii. The big vessels have destroyed the orderly arrangement of fusiform initial derivatives as they have expanded iii. Has more cell types, larger rays 1. Water conducting cells= tracheids and vessels 2. Additional cell types: fibers, axial parenchyma (no associated with resin ducts) 3. Rays larger than those of conifers 4. Can be ring or diffuse porous a. Ring porous trees make very large vessels early in the season; generally only conduct water through outermost growth ring; vessels of smaller diameter later in the growth increment b. Diffuse porous trees scatter uniformly- sized vessels throughout the growth ring; the vessels are diffused throughout the growth increment c. Sapwood vs. Hardwood i. Heartwood: darker, nonconducting wood; contains no living cells; contains secondary chemicals ii. Sapwood: wood that contains living cells; a subset of the sapwood still conducts water iii. All wood begins as sapwood** 1. After some years, sapwood is turned into heartwood via a genetically-controlled process 2. Probably not a “chemical dumping ground” 3. Secondary chemicals it contains are COSTLY to produce 4. Contains secondary metabolites and blocked xylem vessels to repel and impede decay producing fungi iv. Heartwood formation protects against wood-decaying fungi 1. Wood rotting fungi spread through the trees by traveling up through the empty xylem tubes 2. Non-functional xylem filled with toxic secondary metabolites 3. And also physically occluded with gums (conifers) and tyloses (angiosperms) a. * Tyloses are balloon-like outgrowths of ray or axial parenchyma cells that grow into the lumen of nonconducting xylem vessels, physically blocking them b. Prevent spread of pathogens through nonconducting xylem d. Reaction Wood: i. Special kinds of wood used to right a leaning tree or hold up a heavy branch against gravity ii. Angiosperms: tension wood on top 1. Pull up a leaning stem with tension 2. Tension wood forms on the side of the affected part of the plant, pulling it towards the affected force 3. Composed almost entirely of cellulose iii. Conifers: compression wood on bottom 1. Push up a leaning stem with compression wood 2. The compression wood forms in the bend on the opposite side of the applied force, thereby lengthening/strengthening the bend 3. Compression wood is rich in lignin