Secondary Growth
Vascular and cork cambium activity, annual rings, heartwood and sapwood. (Biology › Anatomy of Flowering Plants, NEET UG syllabus.)
What is Secondary Growth?
Increase in the girth or diameter of the stem and root due to the activity of lateral meristems.
Key points
- Define secondary growth and identify plants exhibiting it.
- Describe the formation and activity of vascular cambium.
- Explain the formation of annual rings and their significance.
- Describe the formation and activity of cork cambium.
Common exam trap
Confusing primary and secondary growth.
Definitions
- Term
Secondary Growth
- Meaning
Increase in the girth or diameter of the stem and root due to the activity of lateral meristems.
- Term
Vascular Cambium
- Meaning
A lateral meristem that produces secondary xylem towards the inside and secondary phloem towards the outside.
- Term
Cork Cambium (Phellogen)
- Meaning
A lateral meristem that produces cork (phellem) towards the outside and secondary cortex (phelloderm) towards the inside.
- Term
Annual Rings (Growth Rings)
- Meaning
Concentric rings in the secondary xylem, each representing one year's growth, formed due to seasonal activity of vascular cambium.
- Term
Springwood (Earlywood)
- Meaning
Wood formed during spring, characterized by wider vessels and lighter color.
- Term
Autumnwood (Latewood)
- Meaning
Wood formed during autumn/winter, characterized by narrower vessels and denser structure.
- Term
Heartwood
- Meaning
The older, central, dark-colored, non-functional part of the secondary xylem, providing mechanical support.
- Term
Sapwood
- Meaning
The peripheral, lighter-colored, functional part of the secondary xylem, involved in water and mineral conduction.
- Term
Periderm
- Meaning
The protective outer layer of secondary growth, comprising phellem, phellogen, and phelloderm.
- Term
Bark
- Meaning
All tissues exterior to the vascular cambium, including secondary phloem and periderm.
- Term
Lenticels
- Meaning
Lens-shaped openings in the periderm that permit gaseous exchange.
Learning objectives
Define secondary growth and identify plants exhibiting it.
Describe the formation and activity of vascular cambium.
Explain the formation of annual rings and their significance.
Describe the formation and activity of cork cambium.
Differentiate between heartwood and sapwood.
Identify the components of periderm and bark.
Explain the function of lenticels.
Prerequisites
Basic understanding of plant tissues (meristematic, permanent).
Knowledge of primary growth and primary vascular bundles.
Familiarity with the structure of dicot stem and root.
Common mistakes
Confusing primary and secondary growth.
Incorrectly identifying the tissues produced by vascular cambium (e.g., secondary xylem outwards).
Mixing up the components of periderm or bark.
Not understanding the functional difference between heartwood and sapwood.
Assuming all plants undergo secondary growth (monocots typically do not).
Keywords
Secondary growth
vascular cambium
cork cambium
annual rings
heartwood
sapwood
periderm
phellogen
phellem
phelloderm
lenticels
dicots
gymnosperms
Practice preview
Which part of the wood is primarily responsible for the conduction of water and minerals in a mature tree?…
easy
What is the primary reason for the formation of distinct annual rings in the secondary xylem of trees growing in temperate regions?…
medium
The conversion of sapwood into heartwood involves several significant changes. Which of the following is NOT a characteristic change associated with heartwood formation?…
hard