32 PLANT PHYSIOLOGY 



definitely established the closest connection between the pene- 

 tration and accumulation of substances in the cells and the 

 process of respiration, which represents the chief source of energy 

 for all intercellular processes. Steward, for instance, observed 

 that accumulation of bromine in the cells of potato tubers takes 

 place only when a sufficient amount of air is bubbled through 

 the solution in which the potato slices are placed. Just what 

 the mechanism of the participation of respiration in absorption 

 and accumulation of substances may be, is not clear. Some 

 authors suppose that there is an adsorption of ions on the outer 

 surface of the protoplast directly in contact with the surround- 

 ing solution. Owing to an internal change of the protoplasm, 

 its particles move with the adsorbed ions to the inner surface 

 and here transmit them to the cell sap. Others think that 

 an important role is played by the carbon dioxide released in 

 the process of respiration which leads to an increase of the 

 hydrogen-ion concentration. These ions are then exchanged 

 with cations present in the surrounding medium. According 

 to this theory, developed chiefly by Lundegardh, anions and 

 cations penetrate independently of each other, using entirely 

 different mechanisms and following different laws. These 

 questions will be returned to when the subject of the absorption 

 of mineral elements by the roots of plants is being examined. 



General References 



Adolph, E. F. "The Regulation of Size as Illustrated in Unicellular 



Organisms." C. C. Thomas, Baltimore. 1931. 

 Belehradek, J. "Temperature and Living Matter." Gebriider Born- 



triiger, Berlin. 1935. 

 Boysen-Jensen, p. "Growth Hormones in Plants." Trans. G. S. Avery, 



Jr., and P. R. Burkholder. McGraw-Hill Book Company, Inc., New 



York. 1936. 

 Bull, H. B. "The Biochemistry of the Lipids." Burgess Publishing 



Company, Minneapolis. 1935. 

 BusGEN, M., and E. MtJNCH. "Structure and Life of Forest Trees." 



Trans. T. Thompson. John Wiley & Sons, Inc., New York. 1929. 

 Child, C. N. "Senescence and Rejuvenescence." University of Chicago 



Press, Chicago. 1915. 

 CowDRY, E. V. "General Cytology." University of Chicago Press, 



Chicago. 1924. 

 Francis, W. D. The crystalUne character of living material. Sciencej 



87: 16, 1938. 



