Question

Tip of twiner is sensitive and coils around support itself. This coiling is called as
A. Nutation
B. Vernation
C. Epinasty
D. Circination

Answer 1

Hint: The plant stem is one of the main structural axes of the plant. It is the important aerial part of the plant and it provides support to the plant and keeps it upright. It bears the other important parts such as the leaves, fruits and the flowers. The stem can be erect or weak in nature.

Complete answer:
The growth of the plant depends upon the growth of the stem. The part of the stem that bears the leaves are known as shoots. Generally, the stem of the plants can be aerial, sub-aerial or underground. The aerial stems are of two types which are erect and weak.
The aerial stems that are weak in nature are known as twiners. The weak stems are very weak, soft and thin in width. They are not able to grow erect or stand erect and for this reason, these plants require some kind of support. Some of the weak stems can be referred to as upright weak stems which are known as twiners or the climbers.
Twiners are long flexible and sensitive stems. The stems coil around the available support just like the rope for an upright support. In twiners, the stem winds around the support which can be a non living structure such as the ropes or rods. The touch sensitive main shot coils around the support and grows upwards. They are very much dependent on the support and the tips are sensitive to the available support. This feature of the twiners is known as nutation.
Nutation is the bending movement of the weak stems that is caused due to differences in growth in different parts of the plant. The twining plants adapt to these movements which helps them to find and twine around the support.
The arrangement of buds and young leaves in a leaf bud before the opening is called a venation.
Epinasty can be described as the nastic movement of the plant during which a part of the plant bends outwards and downwards.
Circination is the circular growth of the leaves or the foliage of a plant.
Thus, the right option is A.

Note: Stem forms the important part of the plant that lies above the ground and remains connected to the roots. It bears leaves, flowers and shows nodes and the internodes region. The plants which bear weak stems and coil around support are called twiners. The tips of the twins are sensitive. In twiners, the movement of the stem takes place due to bending of the stem caused due to mutation which results in coiling around a support.