Transpiration and the Ascent

12
The Ascentof Sap 247
and thickness of leaves, the size of which depends on the storage capacity (capacitance)
of the plant. An example of midday stem shrinkage is shown in
Fig. 7.20 and measurement problems are discussed by Neher (1993). Hellkvist
it al. (1974) published interesting data on vertical gradients of water potential
···intrees, some of which are shown in Fig. 7.19. For example, when transpiration
increases rapidly on a sunny morning the water content and water potential of
-1
-5
o
1200 1800 2400
2 June
Mist
t
4 June
3.2m
45 m
24 1200
A/!Ab,4.~ ~
.ts.