BIO 203 1st Edition Lecture 18 Outline of Last Lecture I Pros and cons of growing bigger II Plant bodies III Turgor pressure IV Sclerenchyma cells V How do trees hold themselves up when they grow sideways VI Three tissue systems VII Bud primordia and axillary buds Outline of Current Lecture I What is secondary growth II Which plants do and don t do true secondary growth III Axial and radial systems IV Secondary growth V Rays periderms and bark VI Gymnosperm wood VII Anthophyte wood VIII Annual Rings Current Lecture I II What is secondary growth a Woody growth durable tissues with chemical composition that make them rigid and resistant to decay b Increase in girth as opposed to length elongation primary growth c Accomplished through the activities of two secondary or lateral meristems Which plants do and don t do true secondary growth a Do i Herbaceous plants ii Tree ferns and palms iii Lack the ability to produce true wood which is formed in distinctive concentric layers b Don t i All the seed plants except monocots ii Ginkgo cycads Gnetales Pinaceae and Cupressophytes iii Shrubs trees and woody vine Anthophyta of all sorts These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV V VI Axial and Radial systems a Secondary growth produces cells running in two directions b Axial system vertically running cells majority of the conducting cells i Big vertical bunch of straws c Radial system horizontally running cells i A few straws stuck horizontally through the big bunch Secondary Growth a Requires two lateral secondary meristems vascular cambium and cork cambium b Vascular Cambium i A cylinder of meristematic tissue that runs through the original vascular bundles ii Develops in a stem that has reached a certain age iii Just like in the original vascular bundles xylem is produced towards center phloem towards edge iv Accumulation of xylem pushes phloem outward destroying the cells quite thin walled v Only thick walled 10 phloem fibers remain intact Rays periderms and bark a Rays i Rays within wood provide horizontal transport and storage ii Living cells iii Phloem rays are triangular filling in the spaces created as circumference increases iv Xylem rays are narrower b Periderms i Kill off older phloem ii Periderms are produced by a second lateral meristem the cork cambium which we will not focus on c Bark i Living and dead secondary phloem ii Outer bark all dead phloem cells iii Inner bark living phloem 1 Removal of inner bark all the way around a tree girdling will kill it Gymnosperm Wood a Relatively simple b Xylem has one type of conducting cells tracheids i Narrow ii Dead at functional maturity c Xylem also has resin ducts i Tubes lined with living cells that secrete resin sap or pitch into duct ii Protects from insects and decay d Ray cells also present living cells run radially primarily for storage VII VIII e Cross section i Cut at right angle to the long axis like chopping a tree down ii Tracheids appear squarish iii Resin ducts iv Rays are lines of thin walled cells v Only one cell wide in gymnosperms f Longitudinal section i Radial section is a cut along a radius of the stem ii Through the midline parallel to rays iii Rays appear as horizontal sets of cells tracheids run vertically Anthophyte wood a Two types of conducting cells i Tracheids similar to those in conifers ii Vessel elements thick secondary walls larger diameter dead when functional b Fiber cells i Hardwoods have lots of fibers c Rays are taller and wider than in gymnosperms Annual Rings a Visible rings mark the end of a year s growth in species in seasonal environments b Result from differences in cell size throughout the year c Early wood spring i Larger cells thinner walls d Late wood fall i Smaller cells thicker walls e The width of each year s growth ring also creates a record of the growth conditions that tree experienced f If you know how a given species responds to climatic variation precipitation temperature the tree rings can tell you about past climate