>>Peter wrote: 4. A saprophyte is automatically walled-off by any living tree.

I don't think so. I think a saprophyte is confined by Compartmentalization zones previous formed. A saprophyte, by definition, lives in dead tissue, meaning that some other event has caused the shedding of the tissue. It is already "walled off". The saprophytes are capable of dissolving only certain components in wood, and are inhibited by active compounds in living tissue and by the compartmentalization reaction zones. So while they are walled off in the sense that they do not penetrate live wood, the zones were already formed by the tree in response to other shedding factors.

Reply to post by Russ Carlson, on February 19, 1999 at 00:38:40:

Russ, We are in alost total agreemnt. What makes a pathogen not a saprophyte? The ability to digest live tissue. And a facultative parasite is somewherre in-between, and a facultative saprophyte is also in-between. But a simple saprophyte is automatically walled off by a living tree... walled OUT of live tissue, into dead tissue. Russ; where does that leave the older xylem, the heartwood, the fiber with hardened-off (non-living) parenchema cells? Are we taling saprophyte? Parsite? Facultative?

Reply to post by Peter Torres, on February 19, 1999 at 00:38:40:

>> RE: Russ; where does that leave the older xylem, the heartwood, the fiber with hardened-off (non-living) parenchema cells? Are we taling saprophyte? Parsite? Facultative?

I'm not sure what you mean by this? What description to give the fungus that is "stuck" behind the 'walled off' section? Does it matter what we call it, if it is confined to the shed tissues?

Reply to post by Russ Carlson, on February 24, 1999 at 00:51:35:

My question relates to "dead" or "non-living" xylem, which is considered dead because the parenchyma cells have lost their protoplam and hardened off. We know this xylem is not inert. To me, "dead" is too strong a term. Your term, "shed tissue" - do you apply that to the xylem (heartwood) I am speaking of?
We should call a fugus that attacks heartwood a "parasite" because it causes a diseased condition by structural weakening.
But if it is truly dead wood, then it can't be a parasite, but it must be a saprophyte.
Does it matter what we call it? It does to me, but I can live with some mystery. Anyway, the way I classify these things in my own feeble mind is that saprophytes cannot, by nature, parasitize live wood. And therefore when they do, we call them facultative parasites.

Reply to post by Peter Torres, on February 24, 1999 at 00:59:59:

I follow Shigo's definition in _A New Tree Biology Dictionary_ on this one, as it makes enough sense. The shed tissue is that which has been segregated from the reactive cells, perhaps by the compartmentalization process. So heartwood is not necessarily "shed" tissue, unless it has been compartmentalized. It no longer reacts with rest of the tree, physiologically. So it can be considered "dead", I suppose.

Shigo points out that only the barrier wall is stationary, the other zones can move or retreat in the face of the fungus. So if the barrier is stable, perhaps the fungus is a saprophyte. If the barrier zone retreats, then the fungus may be considered aggressive, causing a reaction by the host, and therfore is a parasite.

Now doesn't that muddy things a fair bit?

Reply to post by Russ Carlson, on February 24, 1999 at 22:01:19:

I defer to all of you on these issues as you're much more informed than I and it's not my expertise. Might I suggest that we are trying to meaningfully describe and understand processes and that the term "shed" and "dead" may have had specific meanings in other specific inquiries and that moving back to our more common usages may in fact be more descriptive. While actual living processes (reactions?) may only be going on in the outer portions (cambium, sapwood, whatever) we have traditionally used "dead" to describe eather branches which no longer support foliar (and necessarily transport) function and trunk wood (heartwood ?) which is unsound -- succombing to or already succumbed to decay processes. Discolored wood I suppose would be in transition, either relatively rapid or perhaps quite slow. Either it's in the condition that it was laid down and became "heartwood" in or it's something else: dead, discolored, unsound, decayed, decaying. Those fine distinctions MAY help us understand the progression of the biological process but isn't it the physical characteristic we're primarily concerned with in structural analysis?

Reply to post by Scott, on February 25, 1999 at 00:34:53:

Scott, you wrote, "isn't it the physical characteristic we're primarily concerned with in structural analysis?"
In the context of immediate hazard management, yes. In the context of incipient hazard management, I think we should add something to a structural analysis as a caveat, or a warning to prevent misinterpretation.
In order to do that we have to understand the progression of the biological processes of decay and weakness, which of course is assoc. with death, shedding, etc.
I suspect that I need to visit Occam's razor and hone my thoughts. Uneeded terms, whether or not they have definitions, should be discarded for clarity of thought. I will work on that.
I actually thought I was making some progress when I started this thread with "A saprophyte is automatically walled-off by any living tree".
Russ, are you sure that won't work you?

Reply to post by Peter Torres, on February 25, 1999 at 08:05:55:

>>I actually thought I was making some progress when I started this thread with "A saprophyte is automatically walled-off by any living tree".

Peter, I can accept that, if it is used as a (partial) definition of saprophyte. A saprophyte would then be an organism which digests only phyiologically non-reactive cells, or basically those that have been compartmentalized and can be considered dead. I think that saying a tree automatically "walls off" a saprophyte puts the cart before the horse, though.

Once a tree is wounded, it responds by beginning the compartmentalization process. Saprophytic organisms, by the above definition, cannot attact reactive tissue, so therefore cannot initiate the compartmentalization response, but follow it later in time. So the tree is therefore not responding to the saprophyte, but to some other factor. The statement you made implies the tree reacts the saprophyte, which does not seem to be the case.