Vascular Cambium Orientation

[lansing]

I was just wondering why it is that the vascular cambium has evolved so that the phloem is produced external to it whilst the xylem is produced to the inside?

Would the alternate arangement not work as well?

[mith]

Not sure about this but I think the xylem is under more pressure since it is compressed inside the tree, but since it's dead it doesn't matter so much.

[lansing]

ok, does anyone else have more detail or does this sound right?
Are you saying that the pressure on the inner side of the vascular cambium would kill teh phloem cells but this obviously wont bother the xylem?

[Poison]

As much as I know it is about freezing. If xylem was the outer cover, water would freeze easily.
At least, that's what our botany teacher said.

[MrMistery]

Your botany teacher is a very strange person. The suber tissue consists of suberine which is a quite good termoisolant. Lignin also helps. But it is a factor
Still, the main factor, is that because the xylem is on the inside, it helps a great deal for keeping the plant up. Kinda what mithril said about pressure. It is not necessarily the fact that it is dead(but also a factor )about the xylem making it a good sustaining tissue, but the actual structure of the xylem cells
Cheers

[lansing]

Thanks a lot this sounds like the answer. Just one final q, why wouldnt the xylem be able to support the plant from the outside? Because it would constantly be being pushed outwards into the outer bark and lost?

The question i am trying to work out an answer for is:
'Explain why the reverse pattern of growth will doom the plant to death and extinction in the evolutionary race'

[Poison]

Your botany teacher is a very strange person.

Our proffessors say that too, maybe they don't know much about it.

[mith]

What is the reverse pattern of growth?

[MrMistery]

I am guessing xylem on the outside/phloem on the inside.
That is a good question: why wouldn't the xylem be able to support the plant from the outside.. My guess is that if any environment factors harm one side of the plant it will colapse. Thus, with the xylem on the inside it is better adapted. Plus, as Ozge said, there is the factor of water freezing. I have read about this in a book once also, but remain skeptical. Seems logical enough though, because at winter water does not move through the xylem

[mith]

ah I see, it's better to have a solid core than to have a tube