12 MINERAL SALTS ABSORPTION IN PLANTS 



respiration, and schemes linking the physical processes of diffusion, 

 adsorption and exchange to metabolism were proposed. Analyses 

 of sap from vacuoles (see p. 19), showed unequivocally for the first 

 time that both cations and anions can be accumulated by plants 

 against existing concentrating gradients (Fig. 2, cf. Table 4 p. 5) 

 and confirmed the inadequacy of purely physical mechanisms. In 

 spite of extensive investigations, the manner in which respiration 

 participates in the absorption of salt is still far from clear, as the 

 subsequent discussion will show. 



The study of metabolically-mediated ion transport, or "active 

 transport" as it is often called, has gained a much wider biological 

 importance since its first recognition in plants. Active transport also 

 occurs in animals, where it is involved in the contraction of muscle, 

 transmission of nerve impulses, and regulation of the ionic com- 

 position of erythrocytes, body fluids and urine. In animals, an 

 ionic balance is usually established within cells and tissues, whereas 

 in plants the prominent feature is accumulation of salts by growing 

 organisms without the establishment of equilibria. Elucidation of 

 the basic mechanisms of ion transport in biological systems remains 

 one of the most challenging problems to both animal and plant 

 physiologists. 



For further reading 



Gamble, J. L. (1947). Chemical Anatomy, Physiology and Pathology of Extra- 

 cellular Fluids. Harvard University Press, Cambridge, Mass. 

 Mulder, E. G. (1950). Mineral nutrition of plants. Ann. Rev. Plant Physiol. 



1, 1-24. 



Reed, H. S. (1942). Plant Nutrition. In A Short History of the Plant Sciences. 



Chap. 16, pp. 241-53. Chronica Botanica, Waltham, Mass. 

 Sachs, J. von (1890). History of the theory of the nutrition of plants. (Chap. 



2, pp. 445-534). (Translated by H. E. F. Garnsey and revised by I. B. 

 Balfour.) Book III, in History of Botany (1530-1860). 



