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Coriolis deflections in water. In any event, such a situation is
>
> This spiraling growth form of plants is called chirality. Most plants
> that grow in this way spiral counterclockwise although there are a few
> that spiral clockwise. Whichever way they turn, the direction is
> intrinsic to the plant species and under normal circumstances nothing
> can induce them to spiral in the opposite direction. This
> "circumnutation" as the growth is called, takes place via a so-called
> "thigmotactic response," which is a stimulus that allows the plant to
> sense its support and wrap around it. As it begins to helix around,
> the thigmotactic response releases hormones that make the cells on the
> opposite side of the growing stalk elongate and wrap around its support.
>
>
> This growth form seems to have a biochemical basis since researchers
> have been able to change the chirality of a plant species by
> administering depolymerizing drugs that break long polymers into
> shorter ones. A couple of genes called Lefty1sprl and Tornado2 have
> been identified as being associated with the generation of
> chirality. Having said that I don't know that the exact mechanism of
> this in plants is really understood (let me know if you can find
> something!) or what the ecological or evolutionary significance of it
> is. Some researchers (based on experiments on the growth of mosses in
> outer space done on the ill-fated Columbia mission, which miraculously
> survived the crash!) have speculated that a spiral is a very efficient
> way of spreading growth over a wide area. This could ensuring that
> space was optimally filled without parts of the plant crossing over
> each other and blocking light from filaments beneath.
>
>
> For an account of the moss experiments on the Columbia take a look at:
>
>
> http://www.bioedonline.org/news/news.cfm?art=1536
>
> http://weboflife.nasa.gov/currentResearch/currentResearchFlight/spaceSpirals.htm
>
>
>
Hi Chris & All, Jan 27, 2007
This mention of circumnation and Blake's spiral-crossed lovers led
me to dig out some old (1962) notes on Oak phyllotaxy and also reminded
me of some possible confusion in usage.
According to these old notes, Sterling (Amer. J. Bot. 32:380-386,
1945) defined a dextrose spiral as one that rises from left to right on
surface towards observer, sinistrose being from right to left.This
agrees with dictionary definitions and the same convention is used for
right-hand and left-hand threads.
But in the only illustration of twining vines that I could quickly
pull out (Anthology of Scientific German) a "Linkswindender Stengel der
Bohne" shows a pole bean winding from left to right (dextrose or
right-hand spiral) and a "rechtswindender Stengel des Hopfens" shows a
Hop vine winding from right to left (sinistrose or left-hand spiral).
And so that there is a clear contradiction, 'linkswindender' means
winding to the left. Perhaps someone had a bad day or there may be two
usages at one time/place or another.
Getting back to Oak phyllotaxy briefly, having noticed that leaf
scars and bud scales on branches were sometimes right-hand (R) and
sometimes left-hand (L), using thread conventions, I tried to see what
determined this. To make a long story short, it seemed to be largely
determined by an interaction of shoot phyllotaxy and orientation.
Looking from proximal to distal, and visualizing a plot on polar
coordinate paper; on L shoots there were L & R buds in upper left,
mostly R buds on the left side and mostly L buds from the upper right
side around to the lower left side. The distribution of buds on R shoots
was a mirror image of this; L & R buds in upper right, mostly R buds
from upper left around to the lower right side and mostly L buds on the
right side.
Spirals in one context or the other are quite common in plants; e.g.
left-hand hygroscopic spiral thickening in liverwort elaters, left-hand
spiral unwrapping of elaters from Horsetail spores, left-hand spiral
rupturing of some leafy-liverwort sporangia, left-hand spiral
chloroplasts in _Spirogyra_, left and right spiral flattening of some
moss seta and finally left and right-hand spiral thickening of tracheids
& vessels in vascular xylem. Spirals make it possible to fit something
long into a short container and, in some situations, probably increase
strength by replacing side to side bending with twisting.
Yt, DW, Kentville
> Cheers!
>
>
> Chris
>
>
> _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._.
>
> Christopher Majka - Nova Scotia Museum of Natural History
>
> 1747 Summer Street, Halifax, Nova Scotia, Canada B3H 3A6
>
> (902) 424-6435 Email < c.majka@ns.sympatico.ca
> <mailto:c.majka@ns.sympatico.ca> >
>
> _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._.
>
>
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