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I read in a textbook that the vascular cambium creates secondary xylem to its inside and outside. These cells, formerly conducting water, dry out and harden. Their cell walls get lignified creating wood, particularly in the cylinder between cork cambium and vascular cambium. This is actually three related questions.

  1. Is a force exerted on the secondary xylem by the vascular cambium? A force that compresses these cells?

  2. If "yes" to number one, how can soft tissues that make up the vascular cambium press so hard on the previous layers of harder (dried out) secondary xykem? Are concentric cylinders staggered so hardness increases gradually, with a stiffer already compressed cylinder exerting more force than newer secondary xylem cylinders?

  3. The secondary xylem (cortex) is living. Medullary rays traverse them and it is adjacent to the living cork cambium. As lignin is deposited in its cell walls, what biochemical processes continue to occur? The hard walls would deter intercellular transport but the cells must continue interacting.

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  1. No i don't think cells harden because dividing cells apply force on them, if that was true I think it would make more sense for a tree to compress every time more an more as it divides in vascular cambium. What happensn is that it grows in diametar, I think only a few cells of that mass simply can't act on a much more massive body like that. A small ball will hardly move a big wall( given it is not travelling at speed of space shuttle:). Even if that was the case, I still don't see which force would be behing it, there is no gravity in lateral direction. If increasing diametar would provide more an more preassure on the inside than wider trees would have stiffer and stronger middle than tiny ones. And I don't think that is the case.

I am not an expert in botany, this is only my logic.

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  • $\begingroup$ I couldn't understand how soft tissue would exert such a pressure either. $\endgroup$
    – GaryW
    Oct 14, 2023 at 2:10
  • $\begingroup$ That leaves the other questions: what hardens the xylem other than lignin? The cortex is considered alive - how do cellular processes continue when the cell wall is stiff (how do molecules pass through)? The cytoplasm region must still be flexible. It's hard to imagine a soft inside of the cell with a hard cell wall - so hard that a human can't budge even a medium size tree. $\endgroup$
    – GaryW
    Oct 14, 2023 at 2:13
  • $\begingroup$ It is hard to imagine but, cortex is alive. Just like bone tissue, it can be considered alive and yet it is hard as hell. It is like a castle, strong thick walls yet people can live within it just as well $\endgroup$ Nov 16, 2023 at 11:24

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