Question

Successive ring of vascular cambium is found in
(a) Cycas stem
(b) Gnetum stem
(c) Pinus stem
(d) Sunflower stem

• A. Only (a), (b) and (c) are correct.
• B. Only (a) and (b) are correct.
• C. Both (b) and (d) are correct.
• D. Both (a) and (c) are correct.

Answer 1

The correct option is B Only (a) and (b) are correct.

Differential cambial activity during autumn and spring season result in narrow and wide secondary xylem rings respectively which together form the annual growth rings. Temperate plants exhibit cambial activity in spring and autumn seasons, i.e., twice a year. Cambium is more active in spring and forms more number of vessels with wider activities. The increased number of leaves during spring puts a demand for additional vessels to supply sap to new leaves. Autumn season is marked by the lesser number of leaves and hence, decreased sap transport which makes cambium less active. It produces narrow pitted vessels and tracheids. Thus, spring and autumn woods form distinct concentric rings in temperate regions (Cycas and Gnetum). Due to the absence of visible difference between the early and late wood of tropical angiosperms (Sunflower), caused by more or less uniform climate, pores are uniformly distributed throughout the ring. Alpine and cold winter regions are covered with ice throughout the year and thus, no differential activity of cambium of inhabitant species (Pinus) which is a prerequisite for annual growth ring formation.

Thus, the correct answer is option B.