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Trees are not made of wood (How much of a tree is alive?)

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pstotto
898103.  Sun Apr 01, 2012 2:46 pm Reply with quote

Alan Watts said that trees are not made of wood, they are wood. If I remember, little if any of the wood is alive, only a very thin layer of growing substance wrapped around the wood, called bast, the actual tree was just this thin layer and leaves.

 
Sadurian Mike
898107.  Sun Apr 01, 2012 2:58 pm Reply with quote

Humans are also wrapped in dead tissue, yet we are not only alive, but we also class our skin as living.

Are trees not structures which deposit a layer of dead cells around the live core? The tips of the roots and shoots are the ones that grow, but the interior surely has live cells.

 
djgordy
898208.  Mon Apr 02, 2012 4:37 am Reply with quote

pstotto wrote:
Alan Watts said that trees are not made of wood, they are wood. If I remember, little if any of the wood is alive, only a very thin layer of growing substance wrapped around the wood, called bast, the actual tree was just this thin layer and leaves.


Woods are made out of trees though.

Leaves make up part of a tree and they aren't wood.

 
soup
898218.  Mon Apr 02, 2012 4:59 am Reply with quote

djgordy wrote:


Leaves make up part of a tree and they aren't wood.


Not enough of a biologist to posit a case but aren't leaves made of cellulose the same stuff wood is made of? So wood and leaves are both<totally made up word>

 
Efros
898222.  Mon Apr 02, 2012 5:20 am Reply with quote

Cellulose is the support structure of plants, it takes various forms depending on the plant and the part of the plant you look at. The centre of tree trunks are indeed dead, the so called heartwood and is composed of lignin reinforced cellulose enclosed xylem cells. The wood here has changed chemically from the sapwood which surrounds it and the sapwood essentially forms the "pipe" that transports water and minerals from the roots. Just below the surface of the bark are the phloem cells that carry the food from the leaves downwards, the cambium that is the area where growth occurs and the xylem which transports water and dissolved minerals upwards. That is the case for dicotyledons, monocots are somewhat different I think, my botany classes from 40 years ago are growing a bit dim.

 
Celebaelin
898263.  Mon Apr 02, 2012 6:48 am Reply with quote

As plants age the older xylem tubules, which may become ineffective in transpiration due to damage or degradation*, become filled with lignin which stiffens them providing more rigid support. The polymer is obviously not alive in and of itself but then neither is the inorganic component of bone; they are essentially functionally equivalent and few people would draw attention to the fact that the structural components of bone are not alive. Collagen too is a structural extracellular component but I've not seen any specific statement that this component of animal skeletal structure is not alive (strictly it isn't but try living without it). Many terrestrial plants could not grow beyond a very limited height without lignin to support their stems (not sure about large cactus species - they're not very woody AFAIK).

http://en.wikipedia.org/wiki/Vascular_bundle
http://en.wikipedia.org/wiki/Lignin
http://en.wikipedia.org/wiki/Vascular_cambium

The diagram on the right in that last one is useful even though it does look rather too much like an asparagus stalk for my liking (I think it's suposed to be horse chestnut).

* This disrupts the siphoning effect by interupting the continuous column of water from root to leaf.

 
Sadurian Mike
898309.  Mon Apr 02, 2012 8:45 am Reply with quote

Don't cacti rely on being absolutely stuffed with water to maintain cellular rigidity?*


*There I go, pretending that I know about science again.

 
Efros
898321.  Mon Apr 02, 2012 9:04 am Reply with quote

Turgid! Oooer missus!

Although that is undoubtedly a contributor, I think it's the external skin and its ribbing that provides the majority of the support for a cactus.

 

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