Salt relations of woody tissues. - I. Experiments with disks of wood

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Abstract
Solutions of electrolytes when passing through the xylem undergo change in composition through interchange of ions with the walls of the cells, living and dead, and with the contents of the living cells. This interchange has been investigated in thin transverse sections of wood (mainly yew) in solutions labelled with radioactive isotopes (mainly 42K and 82Br). The uptake is assumed to proceed from the external solution via the "water free space" (WFS) to the "Donnan free space" (DFS) and the vacuoles of the living cells; for washing out the reverse. Of the total volume of yew wood about 37% is solids, about 4% is living cells, about 55% is WFS leaving about 4% DFS. The concentration of weak non-diffusible acid in the latter is about 0.8 equiv. l.-1 and its pK between 2 and 3. The velocity constant for the loss of 42K from WFS to DFS is about 10-2s-1 when the wood is in equilibrium with 20 m[image] KCl. It is greater when the concentration is smaller and the potential difference between WFS and DFS is greater. The Q10 of this constant is about 1.9. The efflux of potassium from the living cells is about 0.2 pequiv. cm-2 s-1.

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