CHAPTER 8: STRUCTURE OF WOODY PLANTS

Concepts

Wood in Three Dimensions

Secondary Growth in Roots

Having Multiple Bodies in One Lifetime

Outer Bark

Vascular Cambium

Thinking about the Growth of Wood

Secondary Xylem (Wood)

Secondary Phloem (Bark) #

Anomalous Forms of Growth

Dendrochronology - Tree Ring Analysis

Primary Growth

Secondary Growth

apical meristems

primary tissues

vascular cambium #

cork cambium #

secondary tissues

woody plants

herbaceous plants

taller

wider

wood

bark # #

(mostly) set vascular capacity

increasing vascular capacity

Fusiform Initials

Ray Initials

Initiation of the Vascular Cambium

Arrangement
of Cambial Cells

fascicular cambium

between metaxylem and metaphloem

interfascicular cambium

between vascular bundles

types of cells

fusiform initials #

ray initials #

extended each year

parallel wall cell division

periclinal wall

cambium cell

vascular cell

inner cell

outer cell

secondary xylem

secondary phloem

fusiform initial

bark

wood

increase greatly in diameter

pushes cambium outwards

perpendicular wall cell division

anticlinal wall

increases number of cambial cells

increases circumference
of cambium

necessary because xylem pushes out #

short and cuboidal cells

long, tapered cells

periclinal cell division

cambial ray initial

vascular cell

xylem parenchyma

phloem parenchyma

produce short cells

storage parenchyma

ray initials

short verical rows

width

uniseriate

biseriate

multiseriate

fusiform initials

regular horizontal rows

storied cambium

irregular; no horizontal pattern

nonstoried cambium

shorter fusiform initials

fairly constant distribution of ray and fusiform initials

Growth Rings

Heartwood and Sapwood

Types of Wood Cells

Reaction Wood

tracheids, vessels elements, fibers, sclereids, parenchyma

axial system

derived from fusiform initials

radial system

derived from ray initials

sections

Radial section

Tangential section

Transverse (cross) section

pine wood contains only tracheids

oak wood has vessels

contains tracheary elements

longitudinal conduction of water

fibers

large amount of fibers

hardwoods

basal angiosperms and eudicots

little or no fibers

softwoods

conifers

columns of xylem parenchyma

temporary reservoir of water

woody angiosperms

only parenchyma

rays

functions

conduct material radially over short distances

store carbohydrates during dormant periods

types of ray cells

upright cells

procumbant cells

no direct connection with axial cells

adjacent to axial parenchyma

plasmodesmata

adjacent to axial tracheid or vessel element

tracheary elements have pits in secondary wall

ray cell has thin walls facing pits

stored starch first to be digested

stored starch not digested until later

conifers

almost exclusive uniseriate

ray parenchyma

ray tracheids

horizontal, rectangular cells

secondary cell walls

circular bordered pits

protoplasts

strongly seasonal climates

classic arrangement

early wood

high proportion of wide vessels

or wide tracheids in conifers

late wood

lower proportion of vessels

more mechanical strength

cambium starts dormant

numerous fibers

narrow thick-walled tracheids in conifers

cambium becomes dormant again

annual ring

growth ring

high capacity for conduction

alternate arrangement

vessels form throughout growing season

vessels restricted mainly to early wood

diffuse porous

ring porous

growth rings are indistinct

heartwood

sapwood

center

darker

drier

more fragrant

moister

outer

lighter

water columns break

cannot conduct water

plug

tylosis

decay-resistant heartwood

new layer of sapwood each year

one ring converted to heartwood each year

counteracts stress from gravity on lateral branches

angiosperms

upper side of branch

tension wood

fibers exert tension on branch

prevent from drooping

may contract

lifting branch to vertical orientation

Conifers

underside of branch

compression wood

hearwood and sapwood

growth rings

axial system

radial system

conduction up and down stem or root

angiosperms

conifers

sieve tube members

companion cells

sieve cells

fibers and nonconducting parenchyma

fibers and nonconducting parenchyma

size, shape, and number of rays matches xylem rays

produced by the same ray initals

parenchyma cells used for storage

secondary xylem

secondary phloem

Cork and the Cork Cambium

Lenticels and Oxygen Diffusion

Initiation of Cork Cambia

circumferential stretching

new cambium

cork cambium

phellogen

cuboidal cells

periclinal divisions

inner cell

remains cork cambium

outer cell

cork cell (phellem)

sometimes produces inside layer of parenchyma

phelloderm

phellogen + phellem + phelloderm = periderm

maturation

encrust with suberin

waterproof and chemically inert

cell death

nothing digestible or nutritious left

periderm stretches

cork cells cannot expand much

every few years, new phellogen must be produced

several layers of cork build up

some cells convert to sclereids

inner and outer bark

outer bark

outside innermost cork cambium

inner bark

secondary phloem between vascular cambium and innermost cork cambium

impermeable cork

blocks absorption of Oxygen

interferes with respiration

rounded cork cells

intercellular spaces

diffusion pathway

aerenchymatous cork

lenticels

protrude outward

first cork cambium arises

stems

color changes from green to tan

first bark

arises in epidermis

contains periderm, and cuticle

very smooth

arises in cortex

contains periderm, cortex, and epidermis

smooth

later bark

arises in scondary phloem

only cork and phloem

bark - Edited

secondary phloem

secondary xylem

vascular cambium

cork (phellem)

cork cambium (phellogen)

phelloderm

periderm

bark

roots of conifers and woody angiosperms

vascular cambium

like interfascicular cambium

parenchyma and pericycle cells

starts star-shaped

becomes circular

ray and fusiform initials

sapwood and heartwood

ring porous or diffuse porous

root wood and stem wood similar but not identical

perennial roots

first bark arises in pericycle

endodermis, cortex, and epidermis shed

axial and radial systems

carrots and other root vegetables

wood parenchyma

woody plants

animals

primary and secondary

very different

second grows inside of and destroys part of first

puberty

humans

(also teeth)

eels

molting

exoskeleton

crabs

lobsters

beetles

skin

snakes

metamorphosis

caterpillars

butterflies

moths

maggots

flies

tree rings

climate

different climates have different growth patterns

wider rings happened in optimal years

age of trees

compare to wood used in buildings, etc

date the buildings, etc.

floating sequence

Anomalous Secondary Growth

Unusual Primary Growth

Roots of Sweet Potatoes

increased storage parenchyma

numerous vascular cambia

around individual vessels or groups of vessels

increases rate of cell production

Included Phloem

several eudicots

short period of normal growth

cambium cells differentiate into xylem

cells in oldest secondary phloem become new vascular cambium

normal growth

cycle repeats

protects phloem from pests

Unequal Activity of the Vascular Cambium

some woody vines

two sectors are very active

two sectors are mostly inactive

thin, flat, woody ribbon

flexibility

Secondary Growth in Monocots

Joshua trees and dragon trees

vascular cambium arises just outside outermost vascular bundles

produces only parenchyma

secondary vascular bundles

palm trees

trunks don't taper or branch

no secondary growth

trunk is "woody" due to fibers enclosing vascular bundles

establishment growth

stops at some point

plants have localized growth

hair, nails, and skin too