porometer

An apparatus designed to measure the resistance to the flow of air through a leaf in different external conditions. An example is Meidner's porometer, which consists of a Perspex clamp attached to a bulb pipette. The bulb is squeezed flat and the leaf is inserted into, and covered by, the clamp. The time taken for the air to pass through the leaf and inflate the bulb is proportional to the resistance of the leaf and gives an estimate of the degree of opening of the stomata.