Question

Give an account of activity of cambium in the secondary growth of the stem.

Answer 1

Hint: Secondary growth is a type of growth that is caused due to the cell division in the lateral meristems and it leads the stems and roots to thicken. The secondary growth in stems increases the girth and width of the stem. Secondary growth is found in most seed plants, but in the monocots, there is no secondary growth seen.

Complete answer:
The cambium is the layer of actively dividing cells that present between xylem and phloem tissues and it is responsible for the secondary growth of stems and roots. Secondary growth in the stem and roots takes place when the first season is completed which increases the thickness of root and stems.

This cambium is a single layer of cells and those cells are known as initial cells. Several cell layers are unitedly to form the cambial zone. There are two types of tissues found which are involved in secondary growth and they are vascular cambium and cork cambium. Based on the activities of these two types of tissue, secondary growth also occurs in two steps. The first one is the activity of vascular cambium and the other is the activity of cork cambium.

During the activity of cambium at the time of secondary growth, the cells of medullary rays build strips of cambium and it is called the interfascicular cambium, which produces a ring-like structure. This ring activates when the new cell formation begins and outer side cells are modified into the phloem and the inner side cells are modified into the xylem. This phloem is known as secondary phloem and composed of sieve tubes, companion cells, and phloem fibres, and the xylem is called secondary xylem which is composed of pitted vessels, tracheid, and xylem fibres. Secondary medullary rays are formed due to the activity of vascular cambium.

During the activity of the cork cambium, secondary tissues are formed. The activity of cork cambium is more effective on the outer side than the inner side. When the outermost layer of the cortex starts to divide, this is called cork cambium which helps in the protection of the inner tissue from the attack of fungi and insects.

Note: Secondary growth of stems and roots are causing due to the cell division in the cambial cells. Cambium is a single of cells which present between the xylem and phloem. It is responsible for secondary growth. There are two types of tissue present in the cambium which are vascular cambium and cork cambium. As the tissue is two types, the activities of secondary growth also take place in two steps; activity of vascular cambium and activity of cork cambium.