Presentation on theme: "Stem Lecture Functions Support of Leaves, Flowers, Fruits"— Presentation transcript:
1Stem Lecture Functions Support of Leaves, Flowers, Fruits Conduction of Water, Minerals, Sugars, etc.PhotosynthesisStorageDefense
2Stems support a display of leaves. Stems orient the leaves toward the light with minimal overlap among the leaves.Asclepias - milkweed
3The stem supports a display of flowers Cercis canadensis - redbud
4The stem supports a display of fruits. The stem of a vine “twines” around objects in the environment - circumnutation!Ipomoea nil - morning glory
5The stem does photosynthesis… and stores water.Opuntia-prickly pear
6This stem does photosynthesis, stores water, but also produces a defense chemical: mescaline…a hallucinogen.Lophophora williamsii - peyote
7Structure to Provide Functions Stem LectureStructure to Provide FunctionsSupport of Leaves, Flowers, FruitsConduction of Water, Minerals, Sugars, etc.PhotosynthesisStorageDefense
8Typical Stem Cross Section Helianthus annuus-sun flower annualEpidermisCortexA ring of vascular bundlesPith
9Epidermis- window, reduce water lossCortex Collenchyma- extensible supportCortex Parenchyma- photosynthesis, etc.Phloem Fibers- rigid supportFunctional Phloem- conduct sugars etc. away from leaf to rest of plantVascular Cambium- adds 2° xylem and 2° phloemXylemconduct water and minerals up from soilPithwater storage, defense?
10VIP Stem: Provide both name and function labels: Epidermis: reduce evaporation, gas exchangeCortex: photosynthesis, collenchyma supportVascular Bundles: conductionPith: water storage? defense? disintegrate?outsideto centerVascular Bundle:outsideto centerPhloem Fibers: supportFunctional Phloem:conduct CH2O away from leafVascular Cambium:add 2° Xylem and 2° PhloemXylem:conduct minerals up from soil
14Each year the cambium produces a layer of secondary xylem and a layer of secondary phloem. This photo shows secondary xylem from parts of three years in Pinus strobus (white pine).spring of the next yearwinter of that yearfall of that yearmid-summer of one year
15Three years of Secondary Growth Tilia - basswoodSecondaryPhloemcambiumSecondaryXylem
16The study of the growth rings in wood: Dendrochronology
17This tree is Pinus aristata (bristlecone pine). One individual of this species shows more than 5000 growth rings!Inner wood, harvested by boring, was used to validate carbon-14 dating.Imagine the stories that this California tree could tell…perhaps something of migration of Asian peoples down the western coast of North America! They were contemporaries of Pharaohs!
18The epidermis will be stretched and torn if not replaced Sambucus canadensis - elderberry
19A cork cambium differentiates and produces a periderm. EpidermiscutinsuberinCork CellsCork CambiumPhelloderm
20Over time, the epidermis dies. The cork cells build up to for a thick layer for the bark of a tree. We use this to make stoppers for wine bottles and so on.When suberin is fully developed, the cortex cells will eventually be in the dark. So these chloroplasts will lose their function!
21The thick periderm can be quite thick and assist in survival of forest fires! Sequoia sempervirens - giant sequoiaRandy is about six-feet tall!
22The bark covers and stiffens the spines on many woody trees and shrubs.
23Bark =epidermis + periderm + cortex + phloem + vascular cambiumWood =secondary xylem only!Pith =a small percentage of tree diameter at maturity