Question

Spring wood (early wood) differ from autumn wood(late wood) in
A. Size of vessels and tracheid
B. Thickness of cell wall
C. Amount of wood
D. All of the above

Answer 1

The activity of the cambial ring is not uniform throughout the entire year but markedly affected by the variations in the external environment i.e. climate as well as internal environment of the plant.

Complete answer:
In temperate regions like Asia, North America etc the climatic conditions are not uniform throughout the year and different seasons show different climates. The secondary xylem of the wood produced in different seasons due to the differential activity of cambial.

Spring wood	Autumn wood
In the spring season, cambial is very active and produces a large number of xylary elements.	In the winter season, Cambial is less active and as a result fewer xylary elements are formed.
The vessels are produced with the wider lumen as more water is needed to meet the requirements.	The vessels have narrow lumen as less water is needed in this season.
The wood formed during this season is called earlywood.	The wood formed in this season is called latewood.
The springwood is lighter in color and has a lower density.	Autumn wood is darker in color and has higher density.
The transition from springwood to autumn wood is slow.	The transition from an autumn wood to springwood is fast.

The two kinds of wood (spring and autumn wood) that appear as alternate concentric rings of light and dark colour constitute an annual ring. Therefore one annual ring has one circle of spring and a unique circle of autumn wood.
Hence, the correct answer is option (D).

Note: The annual ring represents one year, it is called a growth ring because as the growth keeps on taking place this annual ring keeps on increasing in numbers. One annual ring is the combination of one ring each of the spring and autumn wood seen by the difference in colours.