|Is this twining plant, seen here climbing a|
she-oak, right-handed or is it left-handed?
I explained the basics of this in My Silence Has a Reason in late February. Yesterday, I drafted The Man Who Lost a River, but that's a side issue, except that it means I'm busy.
Now let us return to our moutons. Snail shells have two forms, left-handed and right-handed, as explained in Handedness in shells.
Any helix can twist in the same two ways. An ant going up a right-handed helix standing on its end, moves to the right as you watch it, until it disappears around the back of the helix, while an ant going up a similar left-handed helix moves to the left as it crosses the front of the helix.
Ordinary bolts and screws are right-handed, but gas fittings have left-handed threads. There is a good reason for that, relating to safety, which I leave it to the reader to work out.
Every climbing plant must twine one way or the other to get a grip as it climbs. If it twined first one way and then the other, it might unwrap.
Two brilliant British comedy performers, Michael Flanders and Donald Swann, wrote and performed a song called Misalliance. It was about a love affair between the right-handed honeysuckle and the left handed bindweed.
A web search on <Flanders Swann Misalliance> will turn up several versions. To get the original, add the word hat, because the song was featured in a show called At the Drop of a Hat. Here is a link to a Youtube version.
Listen to their song, then wander out into the garden or the bush and look for twining creepers. Check to see which handedness is more common, and see if any species can twine both ways, maybe even on different stems of the same plant.
Some many years ago, I checked thousands of Australian shells, both on coasts around Australia and Indonesia, and also in the public displays in the Australian Museum in Sydney, where I was working at the time. This was part of a grand scheme for a holiday workshop on handedness. The dull minds that supervised me could not see the value in this, so in the end, I gave up, in part because I failed to find a single left-handed shell, though I could find tendrils of both handednesses.
Some years later, I was maintaining a general weed-and-pond-life tank and while giving it a clean-up, I realised that the pond snails in the tank, probably introduced with some aquarium weeds that I got from a friend, had left-handed shells.
Why are most Australian shells right-handed, while the northern hemisphere ones are often left-handed? Could it be Coriolis forces, the ones often invoked when the myth is trotted out about sinks, plugholes and toilets in the southern hemisphere? (The myth is UNTRUE!!!). Could it be related to the wat the sun's shadow travels, below the equator? Our sundials have to be reversed from those used in the north...
I can't really see it, but there's an interesting and very challenging research problem there.
I am indebted to John Berriman, who emailed me in August 2013 (when I came in and edited a few bits of this) to draw my attention to an article that was published a year ago. It is S.J. Gerbode, J.R. Puzey, A.G. McCormick, L. Mahadevan, 'How the cucumber tendril coils and overwinds', Science 337, 1087, 2012. As you can see, there is a link to the article in that sentence.
The supplementary material published by AAAS includes movies of tendrils twining which you can see at this second link.
How does a plant "decide"?