Experimental Studies of the Factors Controlling Transpiration

Abstract

Previous work on the factors concerned in controlling transpiration has suffered from excessive concentration on the physical aspects of the process. Ever since the classical experiments of Brown and Escombe (1900) called attention to the nature of diffusive processes in the leaf, experimental work has mainly been confined to investigations of evaporation through pores in diaphragms simulating the epidermis of the leaf as closely as possible. Biological aspects have not been investigated with the same persistency. This may, in part at least, be due to the intrinsic difficulties of exploring the effects of the various factors concerned. Before these may be investigated with any prospect of success, it is necessary to devise methods for changing at will the water content of the leaf and estimating the change in stomatal aperture without destroying the leaf or interfering with its normal functioning. In this Institute, work along these lines was begun long ago by Knight, who first exploited the possibilities of studying with a porometer the relation between transpiration and stomatal aperture. His classical work on Eupatorium adenophorum has now found its way into most text-books of plant physiology, but a continuation of the work, so brilliantly initiated by Knight, awaited a period of 12 years, at which time work on transpiration was recommenced in this Institute. The necessary methods have been devised for carrying out experimental studies and a large body of data has been assembled. These data will be presented in this series of papers. The various aspects of research in transpiration may be divided into five main categories: