Stem Lecture Support of Leaves, Flowers, Fruits Conduction of Water, Minerals, Sugars, etc. Photosynthesis Storage Defense Functions
Mar 27, 2015
Stem Lecture
Support of Leaves, Flowers, Fruits
Conduction of Water, Minerals, Sugars, etc.
PhotosynthesisStorageDefense
Functions
Stems support a display of leaves.
Stems orient the leaves toward the light with minimal overlap among the leaves.
Asclepias - milkweed
Cercis canadensis - redbudThe 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.
PhotosynthesisStorageDefense
Structure to Provide Functions
Typical Stem Cross SectionHelianthus annuus-sun flower annual
Pith
A ring of vascular bundles
Epidermis
Cortex
Epidermis - window, reduce
water lossCortex Collenchyma- extensible support
Cortex Parenchyma- photosynthesis,
etc.Phloem Fibers- rigid support
Functional Phloem- conduct sugars etc.
away from leaf to rest of plantVascular Cambium
- adds 2° xylem and 2° phloemXylem
-conduct water and minerals
up from soilPith-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: supportFunctional Phloem: conduct CH2O away from
leafVascular Cambium:
add 2° Xylem and 2° PhloemXylem:
conduct minerals up from soil
outsi
de
to
center
Vitis vinifera - grape
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 - grapeThe vascular cambium makes 2° tissues:
2° phloem2° 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 yearwinter of that yearspring of the next year
Three years of Secondary Growth Tilia - basswood
SecondaryXylem
Secondary Phloemcamb
ium
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