Hint: Plants are actually much more sensitive to touch than human beings. Human skin can minimally detect a thread being drawn across it. However, some plants have a sense of ouch which is nearly 10 times as sensitive as human skin.
Complete answer: Twinning of tendrils is due to a factor caused by thigmotropism.it is directional growth movement which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in twinning of plants and tendrils, however plant biologist have also found thigmotropic responses in flowering plants and fungi. This behaviour occurs due to unilateral growth inhibition. That is the growth rate on the side of the stem which is being touched is slower than on the side opposite the touch. Sometimes the resultant growth pattern is to attach and curl around the object, touching the plant.
In general, tendrils are able to curve by employing a process known as “differential growth”. This process involves the stimulation of growth in particular regions of tendril. Some cells on the contact side will actually compress, which enhances the curving response. Therefore, the non-contact side begins to elongates faster than the rest of the tendril, while the contact side actually compresses. This causes the tendril to curve toward the side of contact.
Note: In addition, some tendrils even exhibit a type of response which is coiling, which is referred to as ”rapid contact-coiling”. This type of response, as the name suggested, is very rapid. It is caused by changes in cell turgor which alter the shape of the tendril, causing it to curve.