"Most twining plants are adapted to ascend supports
of moderate though of different thicknesses.
Our English twiners, as far as I have seen, never twine round trees...".

Charles Darwin, The movements and habits of climbing plants (1888).

Climbing plants have developed a fascinating array of mechanical strategies to achieve vertical growth without being able to support themselves. Hookers, leaners, weavers, rooters, stickers, clingers, tendril-bearers, or twiners are just a few realizations of the 30 different ways vines manage to grow by taking advantage of their surrounding. Twiners, such as garden peas, climbing jasmines, and morning-glories, are perhaps the most studied of all vines. The growing tip waves around in a circular motion known as circumnutation until it finds an appropriate upright support and then start wrapping around it to extend upward. The tip of the vine keeps nutating and the vine continues its climbing process by forming a spiral around the support. The growth process of twining plants raises many interesting mechanical questions.

Can a given twining plant climb around supports of different sizes?

What is the critical cylinder radius above which a plant is no longer able to twine?

What is the effect of friction in the vine ability to grasp the pole?

Similarly, what is the pressure generated by a plant on the pole?

Whereas most plants such as trees or flowers stems are in compression, a peculiar feature of twining plants is that their stem is in tension.

How is this tension generated?

To answer some of these questions, I have developed with Sébastien Neurkirch a mechanical model for climbing plant attachment. The model is base on the theory of Kirchhoff elastic rods. we assume that the vine is an inextensible, unshearable rods with intrisic curvature and torsion in contact with a cylinder. In 2D the problem can be fully explored and we determine bifurcation points at which the contact with the point is lost. We also performed some 3D analysis (much harder but still doable).

You can find more about this problems in our original Phys. Rev. Lett article or on these sites

• The page that Sébastien made (with more details on the model)
• The Institute of Physics has a nice write-up about the problem (web site, PDF)
• The American Physical Society Focus Web page (web site, PDF)
• A very nice movie from Alex Cobb in Holbrook's lab
• Another nice movie from Roger P. Hangarter at Indiana University (click on Morning glory twining)