Proper aeration is necessary, in most cases, for normal development of plants grown in nutrient solutions. In many research institutions a central air compressor makes air pressure available in laboratories and greenhouses through a piping system. When an air compressor is not available, enough air pressure for the aeration of nutrient solutions or for similar biological work can be obtained with laboratory built equipment, utilizing the hydrostatic pressure of the water piping system. RIKER

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... RIKER (1) describe an apparatus which supplies continuous air pressure, obtained by connecting the exhaust tube of a water suction pump to a bottle or similar container fitted with the proper tubing for air and water outlets. The writers have built the equipment described by these authors and used it for the aeration of plant nutrient solutions. It was noticed, however, that the aerator worked well only when the hydrostatic pressure of the water going into the suction pump was strong and fairly constant. Under conditions of variable hydrostatic pressure it does not work satisfactorily and requires constant regulation. After experimenting with several modifications of similar apparatus, the writers arrived at a simple model that supplies intermittent air pressure and that can be used under almost any condition of hydrostatic pressure. The air pressure thus obtained is enough for the aeration of plant nutrient solutions and probably could be used for other types of work that require aeration. Description of the aerator This apparatus supplies air pressure intermittently. It utilizes the rise of the water level in the interior of a bottle to expel the air and so produce air pressure. When the bottle is full a siphon begins to operate, emptying the bottle; after the siphonage ceases, the water level starts to rise again and air pressure is produced. Adequate air pressure is obtained with this aerator under conditions of variable hydrostatic pressure; even when the flow of water stops temporarily and starts again there is no need of new adjustments. The aerator can be constructed with quart milk bottles or similar flasks. Proper glass or metal tubing is easily obtained in any laboratory. Figure IA is a sketch of the aerator as built by the writers. Important details are the siphon tube and the valve that prevents the reflux of liquid in the air outlet. The lower part of the siphon tube inside the bottles needs to 320 www.plantphysiol.org on May 2, 2019 -Published by Downloaded from