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๐ฌ 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 us see.
What makes a stem grow in girth?
- Dicot stems grow thicker as well as taller over time.
- This is due to actively dividing cells arranged in a ring in the stem.
- They make new cells inside and outside in a concentric way.
- This tissue is called the lateral meristem.
What are annual growth rings?
- A cut tree trunk shows ring-like patterns.
- These are annual growth rings, one set per year.
- Wide or narrow rings show good or poor growth years.
- Counting them tells a tree's age and past climate.
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.
๐ NCERT Question 7 — Plot a graph between
Plot a graph of a teak tree’s age against its diameter and annual rings (Table 3.7).
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โ Test Yourself
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Which meristem increases the girth of a stem?
View Answer
The lateral meristem. -
How are the lateral meristem cells arranged?
View Answer
In a ring inside the stem. -
What can annual rings tell us?
View Answer
The age of the tree and the climate it grew in. -
Why are some rings wide and some narrow?
View Answer
They reflect good or poor growth conditions in that year.
Important Definitions
- Lateral meristem — a ring of dividing cells in the stem that increases girth.
- Annual growth rings — yearly rings in wood that show a tree's age and growth conditions.
