"Malcolm Manners" schreef
Remember too, that unlike animal cells which are mostly alive, most of the
volume of "living" plant cells is also non-living space -- the cell wall
and middle lamella are non-living, as is the vacuole inside the cell --
just a big bag of non-living liquid, so that perhaps 80-90% of each living
cell is actually non-living (part of the apoplast). The symplast -- the
truly living portion of the cell, consists just of cytoplasm and its
organelles, and is continuous throughout the plant via plasmadesmota --
small tubes running across cell walls, linking the cytoplasm and the
plasma membranes of one cell to another. Also inside a leaf, there is
quite a lot of air space -- areas not occupied by living cells. So if you
consider all non-living space in the total volume of a tree, you end up
with quite a lot more than just xylem.

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Yes, good point. (Although dead cells are not limited to the xylem, and the
xylem is not limited to the wood)
PvR