Tendril perversion in the
wild
cucumber
On the left : picture taken in Kazmierz
(1998).
On the right : an illustration from Sach's Text-Book
of Botany (1875).
Tendril perversion strikes Kazmierz!
If you are a lucky owner of a garden, and if in the garden there are some climbing plants, have a close look at their tendrils - the thin things the plant uses to attach itself to a support up which it climbs. Interesting physics governs their behavior. Let me describe what I observed in my garden, in Kazmierz near Poznan, during the hot summer 1998, when my wife seeded a climbing plant known among the local gardeners as the "chinski chmiel". As I have recently found out its proper Polish name is "kolczurka klapowana". The Latin name of the climbing plant is Echinocistis lobata. English gardeners call it wild cucumber - an apt name indeed, if you take into account its behavior.
Growing, becoming longer, the tendrils of the plant move around looking for anything to attach to. When they find such a thing, their ends coil around it. Look at one of such lucky tendrils. At the end of this first step, we see a straight, stretched tendril: two ends of it fixed - one to the stem of the plant; second to the thing.
Now comes the second, very interesting part of the story: the tendril starts coiling. But coiling with two ends fixed is not easy! Try it with a piece of a tube. There is a solution: simultaneous coiling of the two halfs of the tendril to the opposite directions. At the end of the process we see a perfect helix: half of it left-handed, the other half right-handed. See below the picture I have taken.
Tendril perversion in the
wild
cucumber
On the left : picture taken in Kazmierz
(1998).
On the right : an illustration from Sach's Text-Book
of Botany (1875).
The phenomenon has been known for a long time (see figure above on the right) but it was only recently, that a theory of it was formulated. Alain Goriely and Michael Tabor published on the 18-th of February 1998, in Physical Review Letters a paper on the " Spontaneous Helix Hand Reversal and Tendril Perversion in Climbing Plants ". Have a look at it.
If you would like to know more about the problem, in particular, if you are interested in its history (which goes back to Charles Darwin) have a look the PowerPoint presentation (which I prepared for a seminar reporting on the Goriely & Tabor paper) or read the paper we published in European Journal of Physics.
If you want to know all the details of the mechanism via which growing intrinsic curvature forces the tendril to coil into a helix, read the recent paper written by Goriely and McMillen.