Lecture 7 - Stems - Secondary Growth Flashcards
What happens to the width of a plant undergoing secondary growth?
Width increases
Do herbaceous plants undergo secondary growth?
They undergo little or no secondary growth
What plants do undergo secondary growth?
Woody plants
Describe secondary growth in monocots and dicots
secondary growth is common in dicots and is seen in 10% of monocots
What are the 2 lateral meristems of secondary growth?
- Vascular cambium
- cork cambium
Explain stem growth of primary growth
Growth in length of stem
What tissue pattern is produced by primary growth?
Basic tissue pattern
Explain stem growth of secondary growth
Growth in width of stem
What tissue is produced by secondary growth?
Secondary vascular tissue
What is secondary growth useful for?
increasing rate of transportation to expanding shoot
secondary growth increases plant stability which reduces the risk of what?
Lodging
What are the secondary tissues?
Cork, phelloderm, secondary phloem, secondary Xylem
What does the vascular cambium form?
Vascular tissue
Where does division of the vascular cambium occur?
At both fascicular and interfascicular regions
Where is the vascular cambium?
Innermost layer of bark, between the xylem and phloem
How does the vascular cambium grow?
Grow to the inside and outside
Cells on the inside of the vascular cambium are called?
Secondary xylem
Cells on the outside of the vascular cambium are called?
Secondary phloem
What are the 2 kinds of vascular cambium cells?
- Fusiform initials
- ray initials
Describe shape of fusiform initials
Longer than they are wide
What do fusiform initials produce?
Axial (vertical) transport system cells
What are the Axial (vertical) transport system cells?
- Sieve-tube elements, companion cells, sieve cells, albuminous cells, fibers
- tracheids, vessels
What do ray initials produce?
Radial (lateral) transport system cells (vascular rays)
What alls are presentin ray initials?
Parenchyma cells
What shape are ray initials?
Usually isodiametric
Where are ray initials located?
Extend from secondary Xylem to secondary phloem
Ray initials: what is the function of vascular rays?
Pathways for movement of food and water and are storage centers
What does the vascular cambium arise from?
Procambium
What does the fascicular cambium arise from?
Undifferentiated cells between the primary xylem and phloem
What does the interfascicular cambium arise from?
Parenchyma of interfascicular region
What does the production of secondary Xylem and phloem result in?
Formation of a cylinder of vascular tissue
What extends through the cylinder of vascular tissue?
Rays
Is more secondary Xylem or secondary phloem produced during development of secondary tissues?
Usually more secondary Xylem is produced
development of secondary tissues: what happens to primary phloem?
Pushed outward and destroyed
development of secondary tissues: what happens to phloem fibers?
They remain intact
The vascular cambium is __________ in temperate zones.
Seasonal
When is the vascular cambium active and inactive?
Active from spring to fall, inactive in winter
Activity of vascular cambium: describe the Xylem in spring.
Large diameter and thin walls
Activity of vascular cambium: describe the Xylem in summer.
Small diameter and thick walls
What does the pattern of vascular cambium activity produce?
Annual rings
What factors vary the width of individual growth rings?
Light, temperature, rainfall, length of growing season
Growth ring width a good indicator of what?
Rainfall - wide if lots of rain
How can the age of a tree be estimated?
By counting the growth rings at the oldest port of the trunk
What is dendrochronology?
Dating events and climatic changes by comparing growth rings
What kind of trees do not have annual rings?
Tropical trees
What is wood?
Secondary Xylem
What is heartwood?
Wood in the centre of the tree - no longer conducting
What is sapwood?
Wood at the periphery of the stem - actively conducting
Another name for hardwoods
Angiosperms
Another name for softwoods
Conifers
What do hardwoods contain?
Tracheids, vessels, fibers, parenchyma
Describe the rays of hardwoods
Larger
What do softwoods contain?
Tracheids, parenchyma, may have resin ducts
Where is bark?
All tissue outside the vascular cambium
What does inner bark include?
Secondary phloem
Where is inner bark?
Inside the innermost cork cambium
Inner bark contains ______ tissues
Living
What is inner barks function?
Conducts food
What does outer bark include?
Periderm
Where is outer bark?
Outside the innermost cork cambium
Outer bark contains ______ tissues
Dead
What is outer barks function?
Provides protection
What is the periderm?
Dermal tissue of the secondary plant body
What does the periderm replace?
The epidermis
Why is the periderm needed?
The increase in diameter of the stem causes the epidermis to crack and split open
What is cork produced by?
Cork cambium
What happens to cork as the stem diameter increases?
Increases in diameter
1 year old stem: what happens to cortex cells under the epidermis?
Become meristematic- produces cork cambium
1 year old stem: cork cambium produces what to the outside and inside?
Outside - cork cells
Inside - phelloderm
Describe cork cells
Flattened and have waxy suberin in cell walls
What is cork cell function?
Seal stem against water loss, insects, bacteria, and fungi
At the end of one year, the stem contains:
- Remnants of epidermis
- periderm
- cortex
- primary phloem
- secondary phloem
- vascular cambium
- secondary Xylem
- primary xylem
- pith
Stems 3-4 years: a new ___________ forms because the old one dies
Cork cambium
Stems 3-4 years: where does the new cork cambium form?
Outer region of the still living phloem
Stems 3-4 years: what happens to old secondary phloem?
Gets separated from the rest of the phloem by the new periderm and is sloughed off
What can damage the vascular cambium? What can the damage lead to?
A porcupine girdling a tree breaks the outer bark and they eat the phloem. This can lead to death of the tree
What are the external features of woody twigs?
Buds, stem buds, bud scales, bud scale scars, leaf scars
Describe buds
Small swellings or bumps on the stem around a node
What tissue do buds contain? What will they develop into?
Meristematic tissue that will develop into a stem, leaf, or flower
Stem buds are apical (terminal) if?
They are at the top or end of a stem
Stem buds are lateral (axillary) if?
If in a leaf axil
What are bud scales?
Modified leaves that cover the buds during winter dormancy
How do bud scale scars occur?
When the bud breaks dormancy in the spring and the scale falls off.
What can bud scale scars determine?
The age of a twig
What can you see at the locations where leaves were attached?
Leaf scars
Most monocots __________ secondary growth
Do not have
Monocot: Some palms undergo secondary growth called?
Diffuse secondary growth
Monocot: what do parenchyma cells of ground tissue do?
Continue to divide and expand for a long time. Also an increase in size of intercellular spaces