PLANT CELL GROWTH AND NUTRITION 457 



Against this background, some salient problems of plant physiol- 

 ogy will now be examined. The topics to be discussed are drawn from 

 the following areas: 



1. Cell physiology in relation to the absorption and movement of 

 solutes. 



2. The role of cellular organization in the metabolism of growing 

 and non-growing cells. 



3. Cell physiology in relation to morphogenesis. 



In each of these areas there is a need to know more about the 

 milieu in which physiological events occur and to understand how rela- 

 tivel)- simple molecules or stimuli may often influence the behavior of 

 relatively complex systems. 



Some problems of ion absorption and movement 



This area of cellular and plant physiology furnishes excellent ex- 

 amples of the thesis enunciated above. From the classical period to 

 m^odern times the problems presented' by the composition of the in- 

 ternal aqueous environment of cells and of organisms in relation to the 

 quite different— and usualh' very much more dilute— solutions with 

 which the\' are bathed ha\e been apparent. And the movement of 

 solutes— organic and inorganic— oxer relatively long distances in the 

 plant body has also been a challenging problem. For recent surveys of 

 these great questions, reference may be made to Steward and Sutcliffe 

 (1959), to Swanson (1959), and to Biddulph (1959). From the factual 

 background there outlined, the following ideas emerge. 



It may seem a simple thing to expect a plant physiologist to 

 explain how a cell absorbs potassium or chloride ions from the environ- 

 ment. Although their immediate sources may be endogenous, rather 

 than exogenous, the secretion and storage of numerous freely diffusible 

 organic solutes in \'acuoles, or aqueous phases, of cells equally requires 

 explanation. It is a familiar fact that when the vital organization is de- 

 stroyed by killing, or its operations are impaired by anesthetics, poisons, 

 or a variety of restrictions upon metabolism, the principles of diffusion 

 reassert themselves, and solute movements toward true equilibrium 

 occur. In other words, and to quote a familiar aphorism, in living cells 

 and organisms the principles of diffusion do not operate in a free and 

 unrestricted fashion. It is these very restrictions upon diffusion that 

 enable the cells and organisms to retain their integrity in their environ- 

 ment, but it is equally obvious that they are due not to passive proper- 

 ties of a quiescent biological system but to the activity of the cellular 

 system as a dynamic molecular machine. 



A most surprising feature of the organization, in a living cell or an 



