. What are the two type cell of Cambium. Explain
The cambium has two types of cells :
(a) The fusiform initials which are elongated form fibres, sieve cells, sieve tubes, and tracheids.
(b) Ray initials which produce parenchyma cells of the rays in wood and phloem.
1. Ray initials are much shorter than fusiform initials.
2. Certain cells of cambium form some narrow bands of living parenchyma cells passing through secondary xylem and secondary phloem and are called secondary medullary rays.
3. These provide radial conduction of food from the phloem; and water and mineral salts from the xylem.
4. Annual rings: Activity of cambium is not uniform in those plants which grow in the regions where favourable climatic conditions (spring or rainy season) alternate regularly with unfavourable climatic conditions (cold water or dry hot summer).
5. In temperate climates, cambium becomes more active in spring and forms greater number of vessels with wider cavities; while in winter it becomes less active and forms narrower and smaller vessels.
6. The wood formed in the spring is known as spring wood and they are formed in the dry summer or cold winter as autumn wood or late wood. Both autumn and spring wood constitute a growth or annual ring.
7. In one year only one growth ring is formed. Thus by counting the number of annual rings in the main stem at the base we can determine the age of a tree. This branch of science is known as dendrochronology.
8. Growth rings are distinct or sharply demarcated in the plants of temperate regions, where as in tropical climate (near equator) they are not distinct or sharply demarcated.