ABSTRACT
This chapter explores the theory used to predict the gaseous exchanges between a plant and its environment. It concentrates upon the entry of carbon dioxide, required by the plant in the process of photosynthesis, and the loss of water vapor from the plant. The exchange of both carbon dioxide and water vapor between the plant and its environment occurs primarily through the stomatal pores. The chapter provides a general review of the resistance concept and presents the historical roots of the method. It focuses on the major contributions to the development of the theory, in contrast to experimental procedures and concerns steady state diffusion, a process governed by Laplace's equation. The chapter emphasizes the assumptions and approximations which are implicit in the resistance model of diffusion. It also provides the equations needed for consideration of the quantitative aspects.
