Anatomy of Flowering Plants Test - 80

Girdling is the technique of removing (peeling) of bark from the branch or trunk area of a tree. This technique was developed to disrupt sugar transport in phloem, stimulating early flowering and increasing fruiting, and for controlling plant size. It also reduces the need for pruning. During this process, the cork cambium, phloem, cambium and sometimes xylem are also removed with the bark. Xylem is left untouched in most of the cases, due to which water and minerals are transported from the roots to the leaves.  As phloem is removed, sugar is not transported from the leaves to the roots which results into the death of the roots. When the roots cannot produce ATP and transport nutrients through the xylem, death occurs. 

The waterproof waxy substance present in the higher plants are known as suberin. Suberin is a main constituent of cork and is named after the cork oak, Quercus suber. Its main function is a barrier to movement of water and solutes. Suberin is highly hydrophobic and a somewhat 'rubbery' material. 

Cycas and Gnetum are gymnosperms and show wide range of distribution from tropical rain forest to temperate and desert i.e. they are found in the places showing clear transition of season from winter-autumn-summer-spring.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 cavities. The increased number of leaves during spring puts a demand for additional vessels to supply sap to new leaves. Autumn season is marked by 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. Due to absence of visible difference between 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 which is prerequisite for annual growth ring formation. Pinus is present in alpine, snow covered regions where winters last for  months in a year and there is no clear demarcation of different seasons. 
Therefore, the correct answer is option B.

Cork cambium is a lateral meristematic tissue found in vascular plants and is part of the periderm. This forms in living cells of the epidermis, cortex, and in some plants, phloem. The cork cambium which produces a secondary protective tissue, the periderm is responsible for secondary growth in many woody, herbaceous dicots, gymnosperms and some monocots and replaces the epidermis in roots and stems.

Cork cambium is a tissue found in many vascular plants as part of the periderm. 

Tunica corpus theory was given by Schmidt in 1924. The theory highlights the mechanism of the orientation of cells at the shoot apex. According to this theory, the shoot apex can be differentiated into two regions of unlike structure and appearance, a central core, the corpus with large cells dividing irregularly to result in volume growth. It is surrounded by an outer enveloping layer the tunica. Tunica cells are smaller and divide mainly anti-clinically to result in surface growth. It may have a single layer or multilayer.
Thus, the correct answer is option A.