Question

In autumn, cambium is
A. Inactive
B. Less active
C. More active
D. Killed

Answer 1

Hint:- Cambium is essential for the secondary growth in plants, mainly in dicotyledonous plants. They are lateral meristematic tissues. Vascular cambium and cork cambium are the two meristematic tissues involved in the secondary growth of plants. The activity of cambium depends on physiological and environmental factors. The range of cambial activity is different during the spring season and autumn season in temperate regions.

Complete solution: Cambium cells are actively dividing cells which causes the secondary growth of stem and root. Vascular cambium is responsible for the secondary growth of xylem and phloem which are the vascular tissues. In the Dicot stem, a layer of cambial cells is seen in between the primary xylem and primary phloem. This layer of cambium is called intrafascicular cambium. Intrafascicular cambium is joined together by interfascicular cambium which is formed late constituting the cambial ring. When the cambial ring becomes active it starts to cut off cells. The cells are cut off to inside and outside. Cells cutting off towards the central part form the secondary xylem and the cells cutting off towards the outer part mature into secondary phloem. The cambium actively forms the secondary xylem than the secondary phloem. The phloem cells are gradually crushed due to the accumulation of secondary xylem. Secondary xylem becomes a compact mass. Cambium also produces secondary medullary rays which is a narrow band of parenchyma cells passing radially through the secondary xylem and secondary phloem.
The climatic conditions are not uniform throughout the year in temperate regions. The cambium is very much active and produces a large number of secondary xylem during the spring season. The secondary xylem is the wood part. The wood that is formed during the spring season is called the springwood or earlywood. Likewise, the wood that is formed during the autumn season is called autumn wood or latewood. The cambium activity is less during this climate and forms only a few secondary xylary elements but has a greater density. The springwood is less dense. Due to the continuous action of vascular cambium, the outer layer of the stem gets broken and is replaced by new cell layers by the action of cork cambium or phellogen.
The correct answer is option (B), Less active.

Note:- Cambium is called lateral meristems as they are seen on the lateral parts of roots and stem. In the dicot root, intrafascicular cambium cannot be seen in the early stage, it is completely secondary in origin. Because the vascular bundles of roots are radial. The vascular bundles in the dicot stem are called conjoint open due to the presence of intrafascicular cambium in between xylem and phloem. Secondary growth also occurs in gymnosperms.