Question

A cut trunk shows 26 concentric rings of spring wood and autumn wood in alternate rows. The age of the trunk would be.
A. 13 years
B. 26 years
C. 52 years
D. 104 years

Answer 1

Hint: Primary growth is the growth of roots and stems in the length with the help of apical meristem.
In many dicotyledons plants exhibit an increase in girth and this increase is called secondary growth.
Secondary growth is helpful in woody plants.

Complete answer:
Secondary growth is the outward growth of the plant, making it thicker and wider.
The tissues involved in secondary growth are
1. Vascular cambium
2. Cork cambium
In dicotyledonous stems, during intra stellar secondary growth, a vascular cambium is formed which is known as ring of cambium.
In this xylem is toward the inner side and phloem is toward the outer side.
In the spring or early summer, due to the favorable conditions, a large amount of secondary xylem is formed and it is called Springwood or early wood.
In the autumn season, due to the presence of unfavorable conditions, less amount of wood is formed which is a secondary xylem only and it is called autumn wood or latewood.
Every ring of spring wood and autumn wood together form into an annual ring.
In the 26 rings, 13 rings constitute spring wood and 13 rings constitute autumn wood.
So total 13 annual rings are present.

So, the correct option is option A. 13 years.

Note: Monocotyledons and dicotyledons plants show marked variation in their internal structure.
The secondary growth occurs in most of the dicotyledons roots and stems and which further increase the girth of the organs by the activity of vascular cambium and cork cambium.
The wood is actually a secondary xylem.