462 



PLANT GROWTH AND PLANT COMMUNITIES 



high concentrations of sugar. When salts (KCl or KBr) became avail- 

 able to them, under conditions such that some of the sugar could be 

 metabolized, the cells (as it were) rapidly completed a phase of their 

 arrested growth, turned over much of the stored carbohydrate, and re- 

 placed this solute with the inorganic ions (Figure 3). Thus, by these 

 means, two steps in the normal sequence of development were sepa- 

 rated; namely, the initial secretion of sugar into the vacuole, and its 

 later metabolism and partial replacement by other solutes such as salts. 

 One cannot recapitulate here even the essentials of the work on 

 diflFerent plant systems, recently summarized by Steward and SutclifiFe 

 ( 1959). Suffice it to say that work on thin disks of storage tissue, in the 

 author's laboratories, passed through two main phases. It first showed 

 the diflFerent variables that aflFected the over-all respiration and the 

 accumulation of ions concomitantly, and in this phase of investigation 

 the following implications became clear. It is necessary to maintain the 

 processes of aerobic respiration at the required level to maintain a 

 system with the requisite degree of general activity, but once the cells 

 are in this activated state, they carry out many metabolic processes and 

 are enabled, in the outcome, to take the salt accumulation, as it were, 

 "in stride." The oxidative metabolism is therefore necessary to maintain 

 the whole system in its active state— not merely to contribute the rela- 

 tively minute fraction of the total energy so released that should suffice 

 for the salt accumulation per se. Nevertheless, the metabolic pace of 

 the whole system is clearly linked to the ion uptake of which it is 

 capable. 



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5 10 20 30 40 50 60 70 80 90 100 

 PER CENT OXYGEN IN GAS MIXTURE 



Figure 3. Relation of oxygen tension in flowing gas stream to accumulation 

 of salt by excised barley-root systems. (From Hoagland and Broyer, 1936.) 



