3.2.2 Lateral meristem โ€” How do plants grow in girth?

Last updated at August 14, 2026 by

๐Ÿ’ฌ Think about it

Look at a cut tree trunk and you will see rings.

The trunk got thicker year by year.

So plants grow not just taller but also wider.

Which tissue makes a stem thicker?

Let's see.

What happens if we cut the trunk of a tree?
3.2.2 Lateral meristem โ€” How do - Tissues in Action - [Teachoo] - Concepts
Bark (outer)
Lateral meristem (ring of dividing cells)
Annual growth rings (one set per year)
Wide ring = good year; narrow ring = poor year
  • On the cut surface we see ring-like patterns , one inside the other.
  • These are called annual growth rings .
  • One set of rings is formed each year .
  • Some rings are wide (a good growth year) and some are narrow (a poor growth year).
How can scientists estimate the age of a tree?
  • Scientists count the annual growth rings on the cut surface of the trunk.
  • One set of rings = one year of growth, so the number of rings gives the age of the tree .
  • The width of the rings also tells them about the climate of that year โ€” wide rings mean good growing conditions, narrow rings mean poor ones.
How do plants and trees increase in girth?
  • A trunk gets thicker year by year because new cells keep getting added.
  • These new cells are made by actively dividing cells arranged in a ring inside the stem.
  • New cells are added inside and outside this ring, in a concentric way.
  • This is how the stem increases in girth (thickness) . The tissue that does this is the lateral meristem .
What is the lateral meristem?
Lateral Meristem
Lateral
at the sides โ€” a ring
inside the stem
Meristem
tissue of actively dividing cells
โ†“
The ring of dividing cells that adds new cells inside and outside, so the stem grows in girth.
  • The lateral meristem is a ring of actively dividing cells in the stem.
  • It adds new cells inside and outside in a concentric way.
  • It makes the plant grow in girth .
Where is the lateral meristem found?
part 2 - 3.2.2 Lateral meristem โ€” How do plants grow in girth? - Concepts - Chapter 3 - Tissues in Action (Exploration) - Class 9 (Exploration)
Lateral
Meristem
Where the Lateral Meristem is Found
Lateral Meristem
โ†“
In the stem
arranged as a ring, along the circumference of the stem
Mainly in dicot plants and trees
their stems keep growing
thicker with age
โ†“
It increases the girth (thickness) of the stem.
  • It is found in the stem , arranged as a ring along the circumference of the stem.
  • It is found mainly in dicot plants and trees , which keep growing thicker with age.
Comparison between apical meristem and lateral meristem
Basis Apical Meristem Lateral Meristem
Definition The meristem whose cells divide continuously to increase the length of the plant The ring of dividing cells that adds new cells inside and outside to increase the girth of the plant
Where found At the apex of the shoot and the tips of the roots Along the circumference of the stem , arranged as a ring
  • Both are meristematic tissues โ€” their cells divide actively.
  • The apical meristem increases length ; the lateral meristem increases girth .
Important Points
  • The lateral meristem is a ring of dividing cells in the stem.
  • It increases the girth (thickness) of the stem.
  • Annual growth rings reveal a tree's age and past climate.

๐Ÿ“‹ NCERT Question 7 โ€” Plot a graph between

Plot a graph between the age of a tree (in years) on the x-axis and the diameter of the tree (in cm) along with the number of annual rings formed over time on the y-axis, using the data given in the Table 3.7.
View Answer โ†’
โ“ Test Yourself
  1. Which meristem increases the girth of a stem?
    View Answer Hide Answer
    The lateral meristem.
  2. How are the lateral meristem cells arranged?
    View Answer Hide Answer
    In a ring inside the stem.
  3. What can annual rings tell us?
    View Answer Hide Answer
    The age of the tree and the climate it grew in.
  4. Why are some rings wide and some narrow?
    View Answer Hide Answer
    They reflect good or poor growth conditions in that year.
Important Definitions
  • Lateral meristem โ€” a ring of dividing cells along the circumference of the stem that increases girth.
  • Annual growth rings โ€” yearly rings in wood that show a tree's age and growth conditions.
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