In a plant growing in Shimla, a person observed the presence of 20 rings of wood with larger vessels and relatively light color and 20 rings of darker colour wood with smaller vessels in the cut part of stem. This observation suggests:

In temperate regions, the climatic conditions are not uniform through the year. In the spring season, cambium is very active and produces a large number of xylary elements having vessels with wider cavities. The wood formed during this season is called spring wood or early wood. In winter, the cambium is less active and forms fewer xylary elements that have narrow vessels, and this wood is called autumn wood or late wood. 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. Therefore, we can say that the age of the plant is 20 years.