Key points are not available for this paper at this time.
J. Hellkvist, G. P. Richards, P. G. Jarvis, Vertical Gradients of Water Potential and Tissue Water Relations in Sitka Spruce Trees Measured with the Pressure Chamber, Journal of Applied Ecology, Vol. 11, No. 2 (Aug., 1974), pp. 637-667
Hellkvist et al. (Thu,) studied this question.