On the basis of age, plants are divided into three categories: annuals, bi-annuals and perennials. The annuals are those plants which take birth, grow up, give fruits and die within a year. Wheat, barley, gram, peas, tomato – all live for one year only. The bi-annual plants live for two years. In the first year they bear only leaves, and in the second year – flowers and fruits, and after that they die. Plants like the ‘fox-glove’ and the ‘hollyhock’ come under this category. The perennial plants live for more than two years. Generally they are called trees or bushes. They blossom and bear fruits many times. The trees of the neem, mango, jamun (black plum), guava etc. come under this category. Some perennial trees have a life of more than 4000 years. The great sequoia trees found in California are reported to have a life of more than 4000 years. The yew trees live for 3000 years. The chestnut and the oak trees live for 2000 and 1500 years respectively.
Now the question arises: how is the age of any perennial tree determined? Scientists have devised a very simple technique to do this. This technique refers to the number of rings present in the trunk of a tree. If you cut off a slice from the tree trunk, you will notice many concentric rings in it. These rings are the record of the tree’s age. In fact, the trunk, underneath the bark, keeps on growing thicker with age. However, the wood which grows in winter and autumn is denser and harder as compared to that grown in spring and summer. This results in the formation of a ring in the trunk every year. These rings are of brown and cream colours alternatively. Thus the number of rings counted from the centre of the trunk of a tree tells its age in years. Its central portion is called the ‘path’.