If a tree of temperate region shows 20 rings of light colour secondary xylem alternating with 20 rings of dark colour secondary xyelm then the age of tree is

The spring wood is lighter in colour and has a lower density whereas the autumn wood is darker and has a higher density. The two kinds of woods that appear as alternate concentric rings, constitute an annual ring. Annual rings seen in a cut stem give an estimate of the age of the tree. Therefore, if there are 20 rings of light colour and 20 rings of dark colour the age of the plant is 20 years.