464 PLANT GROWTH AXD PLANT COMMUNITIES 



investigations of roots, attached and unattached, by other schools of 

 thought. This has been summarized in the chapter already mentioned 

 (Steward and SutcliflFe, 1959). What does seem to be profitable is to 

 recapitulate in their present form the results of the investigations re- 

 ferred to above. 



The essential ideas expressed above largely antedated ( 1930 to 

 1940) our present views on phosphate-bond energy and on the now- 

 familiar concept that specific phosphorylated compounds, generated 

 incidentally to carbohydrate breakdown, can apply their energy at 

 specific points to do chemical or physico-chemical work. It is now 

 natural to assume, therefore, that some part of the energy released in 

 over-all respiration— a part which would be related to and a function 

 of the whole— could be specifically directed to the energy-requiring 

 processes of the accumulating cells, i.e., to protein synthesis and/or to 

 ion intake. One still sees, therefore, the energy delivered, as it were, in 

 a similar package for the process of ion accumulation and for the pro- 

 tein synthesis which is its so frequent concomitant. Only if the energy 

 is so linked does the relation between carbon dioxide output and ion 

 intake appear. In fact if, in a number of ways that have been described, 

 the "metabolic clutch" that throws the cellular engine into gear is dis- 

 connected, then the energy of respiration runs to waste. In these cir- 

 cumstances, neither renewed protein synthesis nor ion intake ensues; 

 on the contrary, the cells may fail to retain their previously absorbed 

 ions against water. For potato disks this is the condition that obtains 

 after long storage of the intact tubers at low temperature, or if disks 

 from normal tubers are treated at pH 7.0 with relatively high concen- 

 trations of carbon dioxide, or if they are exposed to low concentrations 

 of dissolved oxygen. This condition, characterized by inability to ac- 

 cumulate solutes, is one which some cells normally approach in the 

 culminating phases of their development, as, for example, in the cells 

 of certain fruits, especially after the climacteric has passed, or in cer- 

 tain organs of monocotyledons that contain cells which can no longer 

 grow. One now sees, therefore, the salient problem of salt accumula- 

 tion to be the precise location in the cells of the site at which the 

 metabolic energy is donated by a specific and identifiable energy-rich 

 compound produced by, and a function of, the aerobic respiration of 

 the cells. It would be consistent with the discussion thus far if the site 

 in question could involve simultaneous effects upon ion intake and 

 protein synthesis. 



Cells vs. organelles (mifochondria) . But how do these views fit 

 into modern ideas about cells and their organization? A popular trend 

 is to see how far the various physiological and biochemical events can 

 be attributed to, or recapitulated in, the particles that can be isolated 

 from cells. For the problems of salt accumulation by cells this would 



