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Deciduous Trees

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32543.  Sat Nov 19, 2005 3:54 am Reply with quote

There are an awful lot of these johnnies, so we ought to be able to come up with something.

Thought i would join eggshaped trying to make this forum a little plumper especially as the Great Unwashed have started posting non-D threads on the outsdide 'D' forum...

33133.  Mon Nov 21, 2005 6:25 am Reply with quote

The mechanism by which leaves fall is quite interesting.

Leaves fall because they are 'expensive' energy-wise (this is the reason why most biological adaptations exist), and it's not worth keeping them around in winter when there's not much light around in the temperate zones.

Chlorophyll, which is what gives leaves their normal green colour, is a valuable molecule, and the tree can't afford to lose its constituents, having spent all that time and energy making it. The tree breaks it down for the nitrogen, phosphorous and magnesium atoms in it, pulling them back out of the leaves.

This is why the leaves turn orange, red and yellow - beta caroteins (the same things that keep flamingoes pink and carrots orange) are always present in the leaf, but chlorophyll 'masks' their colour. With chlorophyll broken up and removed, the 'spectacular autumn colours' shine through.

At the base of each leaf stalk, a special layer becomes active which breaks down the cell walls that normally keep the juices flowing into and out of the leaf. The dry stem and leaf falls away, and the twig creates a tiny cork (literally made from cork) to seal up the tubes.

Some tropical trees are also deciduous, to coincide with the rainy and dry seasons there (rather than the light/dark seasons of temperate zones).

33134.  Mon Nov 21, 2005 6:31 am Reply with quote

If you say so, though in light of the intelligent plants hypothesis advanced in another forum, I was persuaded that they were simply changing their colour preferences and leafiness choices in response to changing fashion in the arboreal world. IE, one does it, so they all do.

Pre-war school philosophy exam question mentioned on Desert Island Discs yesterday:
"Nature is poorly lit and too green." Discuss.

33139.  Mon Nov 21, 2005 6:54 am Reply with quote

If trees had eyes, went in for sexual selection, and were mobile then I suppose it might be possible... As it is, their 'drop your seeds' method seems a somewhat simpler explanation, and accounts for the excellent adaptive shapes of plant seeds.

33140.  Mon Nov 21, 2005 6:57 am Reply with quote

...too green

It seems almost suspiciously exactly green enough to me. :-)

33154.  Mon Nov 21, 2005 8:06 am Reply with quote

I live in the countryside, and I do find nature's use of green a bit indiscriminate. A few trees have red leaves, and they always cheer a garden up, I think.


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