Question

Which of the statements given is not true about the formation of annual rings in trees?
A) annual ring is a combination of springwood and autumn wood produced in a year
B) differential activity of cambium causes light and dark bands of tissue early and latewood respectively
C) activity of cambium depends upon the variation of climate
D) annual rings are not prominent in trees of temperate region

Answer 1

Some plants mainly dicotyledons exhibit an increase in girth. This type of mechanism is called secondary growth. The annual rings are concentric rings that result due to cambium. The cambium is more active in the spring season.

Complete answer:
Annual rings and growth rings are formed due to fluctuations in the activity of cambium. Cambium is the meristematic layer responsible for the cutting of vascular tissues that is xylem and phloem. Initially, it is present in patches as a single layer between vascular bundles. Later, during the development, it forms a complete ring. Cambium is very active in the spring season resulting in a large number of xylary elements having vessels with wider cavities. The wood formed during this season is called springwood or earlywood. The cambium is less active in winters and forms fewer xylary elements having narrow vessels, and this wood is called autumn wood or latewood. The springwood is lighter in colour and has a lower density as compared to the autumn wood; autumn wood is darker and has a higher density. The two kinds of wood that appear as alternate concentric rings, constitutes an annual ring. Growth rings are formed by the seasonal activity of cambium. In a plant of temperate regions, cambium is more active in spring and less active in the autumn season. In temperate regions, climate conditions are not uniform throughout the year. However, in tropics, climate conditions are uniform throughout the year. Thus, annual rings are prominent in trees of temperate regions.
Hence, the correct answer is option D.

Note: Annual rings give an estimate of the age of trees. The cambial rings cut off new sales towards inner and outer sides. The activity of cambium is dependent on many psychological and environmental factors. These annual rings show the amount of wood produced during one growing season.