Presentation on theme: "Stem Lecture Support of Leaves, Flowers, Fruits Conduction of Water, Minerals, Sugars, etc. Photosynthesis Storage Defense Functions."— Presentation transcript:
Stem Lecture Support of Leaves, Flowers, Fruits Conduction of Water, Minerals, Sugars, etc. Photosynthesis Storage Defense Functions
Stems support a display of leaves. Stems orient the leaves toward the light with minimal overlap among the leaves. Asclepias - milkweed
Cercis canadensis - redbud The stem supports a display of flowers
Ipomoea nil - morning glory The stem supports a display of fruits. The stem of a vine twines around objects in the environment - circumnutation!
The stem does photosynthesis…and stores water. Opuntia-prickly pear
This stem does photosynthesis, stores water, but also produces a defense chemical: mescaline…a hallucinogen. Lophophora williamsii - peyote
Stem Lecture Support of Leaves, Flowers, Fruits Conduction of Water, Minerals, Sugars, etc. Photosynthesis Storage Defense Structure to Provide Functions
Typical Stem Cross Section Helianthus annuus- sun flower annual Pith A ring of vascular bundles Epidermis Cortex
Epidermis - window, reduce water loss Cortex Collenchyma - extensible support Cortex Parenchyma - photosynthesis, etc. Phloem Fibers - rigid support Functional Phloem - conduct sugars etc. away from leaf to rest of plant Vascular Cambium - adds 2° xylem and 2° phloem Xylem -conduct water and minerals up from soil Pith -water storage, defense?
VIP Stem: Provide both name and function labels: outside to center Epidermis: reduce evaporation, gas exchange Cortex: photosynthesis, collenchyma support Vascular Bundles: conduction Pith: water storage? defense? disintegrate? Vascular Bundle: Phloem Fibers: support Functional Phloem: conduct CH 2 O away from leaf Vascular Cambium: add 2° Xylem and 2° Phloem Xylem: conduct minerals up from soil outside to center
Vitis vinifera - grape
Notice how the vascular cambia of adjacent vascular bundles line up side by side. Notice that cambium tissue differentiates between the bundles, connecting the cambia together.
Vitis vinifera - grape The vascular cambium makes 2° tissues: 2° phloem 2° xylem
Each 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). mid-summer of one year fall of that year winter of that year spring of the next year
Three years of Secondary Growth Tilia - basswood Secondary Xylem Secondary Phloem cambium
The study of the growth rings in wood: Dendrochronology
This 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!
The epidermis will be stretched and torn if not replaced Sambucus canadensis - elderberry
A cork cambium differentiates and produces a periderm. Epidermis Cork Cambium Phelloderm cutin suberin Cork Cells
Over 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!
Sequoia sempervirens - giant sequoia The thick periderm can be quite thick and assist in survival of forest fires! Randy is about six-feet tall!
The bark covers and stiffens the spines on many woody trees and shrubs.
Bark = epidermis + periderm + cortex + phloem + vascular cambium Wood = secondary xylem only! Pith = a small percentage of tree diameter at maturity