Leaf water potential (') and leaf conductance (gl) were measured in the field in 20-year-old olive trees subjected to two treatments of soil water content (dry-farming and drip-irrigation). Differences between treatments of up to 0.35 MPa were observed in predawn , values. At midday, these differences were of up to 0.83 MPa. However, no significant differences between treatments were observed in gl values. Maximum gl values of about 0.77 cm S-l were found early in the morning, clossing the stomata afterwards. In just 12 hours after rewatering following the drought period, the differences between treatments on , values were reduced from 0.29 MPa to 0.14 MPa for predawn values, and from 0.64 MPa to 0.23 MPa for midday values. The recovery was virtually total at the third day after rewatering.

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WITH ONE PLATE SummaryRainfall was measured at an open site and under spruce, pine, and heather. Between 50 and 60 per cent. of the rain penetrated each of the canopies. Variations in the percentage penetration are associated with the area of foliage to be wetted and with the aggregate amount and the intensity of the rainfall. Leyton (1960), and some pre \ iminary data in sites in the Dee Valley, Commission, above sea-level. The characteristics of the vegetation in the areas studied can be summarized as follows : I. A stand of sitka spruce (Picea sitchew's), height 10 m.; canopy almost closed; a layer of litter &out 2.5 cm. thick lying on the soil surface; estimated2 2,480 trees per ha. I Present address: Santo Rey 30, Seville, Spain. This paper includes data which formed part of a thesis (by J. M. A.), approved by the University of Aberdeen for the degree of Ph.D.N.E. of Scotland Conservancy), 7 miles west of Aber 7 een, at 500 ft.

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