A description is given of a modified lysimeter design and sampling procedure designed to prevent edge flow from occuring in large soil monolith lysimeters. An internal cutting ring at the base of the lysimeter casing produced a small annular gap between the soil monolith and the wall of the casing. This gap was filled with liquefied petrolatum, which provided a water-tight seal around the edge of the lysimeter. Water and solutes were unable to leak between the monolith and casing. The use of petrolatum as a sealant is suitable for waterflux and nutrient-leaching studies, but is not suitable for pesticide studies.

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Oocytes of marine and estuarine teleosts often undergo pronounced volume increases during the maturation phase of development that precedes ovulation and fertilization. To examine the physiological correlates of these volume increases, prematuration follicles of the saltmarsh teleost, Fundulus heteroclitus, were cultured in vitro with a maturation-inducing steroid (17 alpha-hydroxy-20 beta-dihydroprogesterone). Mean follicle volume rose significantly (75%) during a 40-h incubation period. Similar to the situation previously found in vivo, uptake of water by the maturing follicle was responsible for this volume increase in vitro, with the water content increasing from 62% to 78% of the total follicle mass. The follicle contents of two probable osmotic effectors--Na+ and K(+)--also rose, the increase in K+ being twice that of Na+. The influx of K+ even exceeded water uptake, resulting in a net increase in the concentration of this cation. It thus appears that the influx of these cations, in particular K+, is a major cause of the uptake of osmotically obligated water and subsequent volume increase experienced by maturing F. heteroclitus follicles. In a search for operant mechanisms, it was found that follicle hydration, but not maturation, was strictly dependent on external K+ in a concentration-dependent manner. The mechanism by which K+ accumulates in the follicle was insensitive to ouabain, so that a typical Na+, K(+)-ATPase mechanism does not appear to be involved. The ability of external K+ to promote follicle hydration was gradually lost during the maturation process as the oocyte dissociated from the surrounding granulosa cells in preparation for ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

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