Cucumber tendrils

Charles Darwin was the first to study cucumber tendrils in the 1860's, and published an extensive book on climbing plants in 1865, which included a section on the tendrils of cucumbers and its relatives of the family Cucurbitaceae. This book entitled "On the Movements and Habits of Climbing Plants" (http://darwin-online.org.uk/converted/pdf/1865_plants_F834a.pdf).

Darwin essentially observed the phenomenon that tendrils adopt the shape of two sections of counter-twisted helices with a transition or kink in the middle (Tendril - Wikipedia (https://en.wikipedia.org/wiki/Tendril).

This phenomenon is illustrated with the following images that I took of cucumber tendrils in the Department of Horticulture and Landscape Architecture greenouse of Purdue University.

When encountering a support, such as a cane, the tendril first wraps around the support:

Once it is tethered in this manner, the tendrils begin to coil in two opposite directions with a kink in the middle:

The coils then tighten:

The physiological basis of this phenomenon was described in a fascinating article published in the journal Science in 2012 (Gerbode, S.J., Puzey, J.R., McCormick, A.G., Mahadevan, L. How the Cucumber Tendril Coils and Overwinds. Science 337 (6098): 1087-1091 (2012): http://science.sciencemag.org/content/337/6098/1087).

"Our experiments on cucumber tendrils demonstrate that tendril coiling occurs via asymmetric contraction of an internal fiber ribbon of specialized cells. Under tension, both extracted fiber ribbons and old tendrils exhibit twistless overwinding rather than unwinding, with an initially soft response followed by strong strain-stiffening at large extensions."

This article was published alongside a time-lapse video and explanatory news article (Underwood, E. Video: How Cucumber Tendrils Curl (2012): http://www.sciencemag.org/news/2012/08/video-how-cucumber-tendrils-curl).

"the researchers found that after the tendril grasps its support, a thin, two-layer ribbon of gelatinous cells shrink on one side as they lose moisture, but not on the other. This asymmetric contraction causes the fiber to wind in opposite directions, creating a spring that may stabilize the plant against large disturbances while permitting it to gently move with small forces, like a gentle breeze. When pulled from either side, the fiber does not unwind like a normal spring, but actually winds tighter. Young, moist tendrils do not tend to overwind, the researchers report online today in Science, but mature, dry tendrils do — helping to explain how delicate tendrils gradually stiffen to support a vine laden with cucumbers."