All the climbing plants and weeds in my garden twine anticlockwise. Is there an evolutionary advantage to this? And do any twine clockwise?
Penelope Reid
Loggerheads, Staffordshire, UK
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I am sure I will be among many of your older readers who recall the tragic ballad of doomed lovers, Misalliance, sung by Flanders and Swann.
In the song, a honeysuckle and a bindweed fall in love and intertwine. Sadly, the honeysuckle鈥檚 parents disapprove because the superior honeysuckles twine to the right and the plebeian bindweeds to the left, leaving any prospective offshoots of the match to be directionless and fall flat on their faces. This and the general disapproval leads to the lovers pulling up their roots and shrivelling away.
Norman Doidge
Newton Abbot, Devon, UK
When looked at from below, bindweed twines anticlockwise while honeysuckle goes clockwise. I fear your correspondent鈥檚 weeds are the former. And good luck controlling that. Is there some evolutionary advantage? Perhaps, but either way is definitely better than not twining at all. 鈥淚t may go straight up and fall flat on its face鈥�, as per Flanders and Swann.
Mike Follows
Sutton Coldfield, West Midlands, UK
In the absence of a skeleton and muscles to articulate it, plants have evolved ingenious ways to move. Instead of growing thick trunks to reach sunlight, climbing plants like sweet peas and cucumbers expend less energy by sending up spindly tendrils. The ends of these tendrils wave around in the air, apparently searching for something to cling onto in a process called circumnutation.
When the end of the tendril encounters something, it twines itself around the support. Once anchored, the rest of the tendril coils up like a corkscrew and, in the process, shortens. This pulls up the rest of the plant.
In 1865, Charles Darwin noted that the upper and lower halves of the cucumber tendril were separated by an untwisted stretch, called a perversion, and that each half had the opposite chirality or handedness (twist direction). Coiling with the same handedness along the whole length of the tendril would have imparted a twisting force or torque, either on the cucumber or its support.
In 2012, a Harvard University investigation (Cucumis sativus) and wild cucumber (Echinocystis lobata) discovered a stiff ribbon of specialised cells inside each tendril. The researchers suspected that cells on one side of the ribbon shortened, bending the tendril in that direction and making it coil.
They observed that the ventral cells (those on the inside of the spiral) produce more of the polymer lignin than the dorsal (outside) cells and speculated that, because lignin is hydrophobic, these cells expel more water and contract more than the dorsal ones. They built a model by bonding together two silicone rubber sheets while one of them was under tension. They then cut the rubber into strips along the strain axis and these mimicked the coiling of the tendrils, including the presence of the perversion.
However, instead of unravelling when stretched as their model did, real tendrils tend to twist even more tightly at first, before eventually straightening with the application of more tension than is expected. This ensures a tighter grip between the climbing plant and its support. It also results in a spring-like connection between the plant and its anchor that acts as a shock absorber in high wind. The team was able to modify the model to replicate this behaviour.
Given that Darwin identified four classes of climbing plant, the Harvard investigation may not be universally applicable to the behaviour of all tendrils.
Jan Henslow
Midhurst, West Sussex, UK
Yes, they do also twine clockwise. Charles Darwin wrote about this in The Movements and Habits of Climbing Plants, of which Ken Thompson鈥檚 Darwin鈥檚 Most Wonderful Plants gives an easy-to-read synopsis, brought up to date. It seems climbers swing around in either a clockwise or anticlockwise fashion until they hit something to wrap around, thus twining in a left or right-handed spiral. Whether they swing to the left or right seems to be just like people 鈥� mostly right-handed but some left ( in plants, apparently).
Elspeth Semple
Inveresk, East Lothian, UK
In my garden, I am blessed with right-handed honeysuckle, but tormented by the beautiful yet persistent left-handed bindweed. So there are climbing plants in the UK that twine clockwise and others that twine anticlockwise.
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