Question

An old trunk of Shisham (Dalbergia sissoo)tree would have the maximum amount of
(A)Primary phloem
(B)Primary xylem
(C)Secondary xylem
(D)Secondary cortex.

Answer 1

An old trunk of a plant means primary growth was already completed and proceeded by secondary growth in the plant cells or tissues. Secondary growth increases the diameter of the stem in plants.

Complete answer:
In Dalbergia sissoo , i.e in dicotyledon plants, during secondary growth primary and secondary meristem join together and form a ring of cambium which is also known as vascular cambium. Its function is to produce wood cells and bark cells. The vascular cambium produces a large amount of secondary xylem towards its inner side.

Additional Information: The primary phloem-Primary phloem is formed during the primary growth of the plant.it is formed from the procambium.
Primary xylem-it od formed first. It is formed during the primary growth of the plant.
Secondary xylem – it is formed from the secondary growth of the plants.
Secondary cortex-It is also formed during secondary growth. It is a living tissue.
Primary growth in plants is responsible for the growth in length and secondary growth is responsible for the growth of the plant in diameter.
In woody plants, secondary growth is equal to the one annual ring. This annual ring helps in determining the amount of wood produced during its period of one growing season.
So, the correct answer is 'Secondary xylem'.

Note: Formation of secondary tissues takes place by the lateral meristem which is of two types i.e vascular cambium and cork cambium. Vascular cambium helps in the production of secondary vascular tissues and cork cambium helps in the formation of the periderm. Cork cambium is also known as phellogen.