When a tree-trunk is cut down, several alternating dark and light bands can be seen. A pair of dark and light band is referred as an annual ring. The annual ring is an indicator of the age of a tree. The older tree, the more the number of rings it will have. The bands in the trunk are light and dark because the wood grows differently in different seasons. The light coloured rings are formed during late spring and early summer when the wood cells are bigger. The dark coloured rings are formed during late summer and autumn when the wood cells are smaller and closely packed.