The Porometer Method for the Continuous Estimation of Dimensions of Stomates

Abstract

In studies concerning the movement of gases and vapors into and out of the leaf, it is frequently necessary that the dimensions of the stomates be determined. Such information may be more useful if it consists of a continuous record of the stomatal aperture rather than a series of periodic measurements. Two methods are generally used for the procurement of such continuous data; direct microscopic measurement and the porometer.Direct microscopic measurement of the dimensions of the stomates has been considered the most accurate method by many workers. There are, however, several difficulties which make accurate measurements by the microscope difficult. For certain leaves, under some conditions, accurate measurements can be made only with extreme difficulty. For other leaves, the microscope cannot be used at all. The method is not well adapted for continuous observation, because of the strain imposed upon the worker and because of undesired changes induced through mechanical manipulation and the use of light. Also, since only a few stomates can be measured at one time, the question arises as to whether they constitute a representative sample or reflect correctly the average stomatal aperture. However, when employed for the determination of the dimensions of the stomates at a particular instant, a high degree of accuracy may be achieved.The porometer is a device used to measure changes in the rate of flow of air through the leaf. A cup or tube is attached to the leaf and the pressure of the air within the cup is either raised or lowered with respect to normal air pressure. It is assumed that the changes in the rate of air flow are directly proportional to the changes in the dimensions of the stomates.The porometer was first proposed by Dutrochet in 1832, according to DARWIN and PERTZ (3). In 1876, Muller constructed an apparatus employing this principle which proved too complicated and cumbersome for general use and acceptance. The modern design for the porometer was developed by DARWIN and PERTZ (3). Improvements were made on this type of porometer by KNIGHT (7), and by LAIDLAW and KNIGHT (9) who devised a constant flow aspirator and made the process self-recording. Other porometers were devised by BALLs (2), and by JoNEs (6). A porometer which measures changes in the rate of flow of air through the leaves in terms of pressure was devised by GREGORY and PEARSE (4). This method uses small rates of air flow and low pressures. It will be described in detail in another section.

The Effect of Some Environmental Factors on the Movements of Guard Cells

“…The writer is unaware of any such published record. Employing the resistance porometer, WILSON (33), records of the stomatal aperture of two species of broad leaf evergreens were obtained from November 1941 through April 1942. Measurements of the light, temperature, and vapor pressure deficit of the atmosphere were also obtained during this same period.…”

An open-andshut case: ABA and stomata

“…Grew 3 , in his 1682 treatise The Anatomy of Plants, first described stomata, well, as stomata; small orifices or 'breathing holes' at the surface of plant leaves. Nevertheless, physiological studies linked stomatal movements to transpiration and plant water relations with the atmosphere only some 70 years ago 4 . Stomata became inextricably bound with the, then newly identified, plant hormone ABA when Wright and Hiron 5,6 at Wye College in Kent, part of the University of London, and Mittelheuser and van Steveninck 7 in the USA, discovered ABA to be highly effective as an agonist to close stomata.…”

The Permeability of Non-Stomate Leaf Epidermis to Carbon Dioxide

“…The leaf cup was sealed with liquid latex to the upper or lower surface of a leaf as described by WILSON (17). The latex coagulated and made a good seal within one hour.…”