b
The cambium activity is seen in the temperate trees in two seasons of the year. In the spring season, cambium activity is highest as a result more amount of wood is formed due to long duration of favourable period. This type of wood is known as spring wood or early wood. In autumn season, cambium activity is arrested as a result dark-coloured, narrow band of autumn wood or late wood is formed. The two woods jointly constitute the annual rings or growth rings.