A) sapwood increases
B) heartwood increases
C) both sapwood and heartwood increases
D) both sapwood and heartwood remains the same
Correct Answer: C
Solution :
The secondary xylem in stem of perennial plants commonly consists of concentric layers. In trasverse section of the axis these layers appear as rings and are called annual rigns or growth rings. The outer region of the old trees consisting of recently formed xylem elements in sapwood or alburnum. This is of light colour and contains some living cells also in the association of vessels and fibres. This part of the stem performs the physiological activities, such as conduction of water and nutrients, storage of food, etc. The central region of the old trees, which was formed, earlier is filled up with tannins, resins, gums and other substances which make it hard and durable, is called heartwood or duramen. It looks black due to the presence of various substances in it. Usually the vessesi remain plugged with lyloses. The function of heart wood is no longer of conduction, it gives only mechanical support to the stem. The sapwood changes into heart wood very gradually. During transformation a number of changes occur-all living cells lose protoplasts; water contents of cell walls are reuduced; food materials are withdrawn from the living cells; tyioses are frequently formed which block the vessels; the parenchyma walls become lignified; oils, gums, tannins, resins and other substances develop in the cells.
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