Experiments were undertaken using growth chamber grown corn plants (Zea mays, L. ) hybrid "United 108," to characterize the relative magnitude of the water-potential in the soil and within the plant. Root water potential was measured in situ with hygrometers attached to the roots (Bnmini, 3); a leaf hygrometer (Neumann and Thurtell, 7; Neumann, 8) was used to measure leaf water potential, and in situ measurements of soil water potential were made with a soil hygrometer (Brunini, 3). The devices are attached to the leaves or roots, or inserted into the soil, allowing continuous measurements of the leaf; root and soil water potential. The results indicate that no apparent damage is caused to the roots by attaching the hygrometers to them. It was also observed that a difference up to 4 bar may exist between the water potential in the root xylem and in the root epidermis. | Se realizaron experimentos utilizando plantas de maíz (Zea mays, L. ) híbrido "United 108" cultivadas en cámara de crecimiento, para caracterizar la magnitud relativa del potencial hídrico en el suelo y dentro de la planta. El potencial hídrico radicular se midió in situ con higrómetros fijados a las raíces (Bnmini, 3); para medir el potencial hídrico foliar se utilizó un higrómetro foliar (Neumann y Thurtell, 7; Neumann, 8), y las mediciones in situ del potencial hídrico del suelo se realizaron con un higrómetro de suelo (Brunini, 3). Los dispositivos se fijan a las hojas o las raíces, o se insertan en el suelo, lo que permite realizar mediciones continuas del potencial hídrico de las hojas, las raíces y el suelo. Los resultados indican que no se causa ningún daño aparente a las raíces al fijarles los higrómetros. También se observó que puede existir una diferencia de hasta 4 bares entre el potencial hídrico en el xilema radicular y en la epidermis de la raíz.

The annual hydrological budget in the montane forest ecosystem of San Eusebio, Mdrida, Venezuela, was studied and water samples collected and analysed for chemical composition. Total rainfall was 1 576 mm, canopy rainfall 1 260 and stem flow 12 mm. The soil water content of the soil and its changes were calculated based on tensiometer readings and pF-curve. An evapotranspiration of 980 nun was calculated from meteorological data. Percolating water was collected with ceramic lysimeters and calculated from above data to be 588 mm. In order to calculate the chemical transfer of elements, 192 water samples were analysed for pH, N, P, K, Ca, Mg, Mn, Fe and Al. The chemical input into the ecosystem depends primarily on the rainfall paterns in the region. The high values for N and Na are related to marine aerosols, gases from petrochemical industries and soil particles. The concentration in the percolating waters are lower than the rainfall, so that there is a chemical accumulation in the ecosystems.