558 SCIENCE PROGRESS 



deut. hot. Ges., 34, 539-554, 1916). For this quantity the present 

 writer is suggesting the EngUsh equivalent of" suction pressure," 

 as by it is meant the net pressure forcing water into the cell, 

 which, when no external forces are operative, is equal to the 

 osmotic pressure of the cell sap less the inwardly directed 

 pressure of the cell wall resulting from its tendency to contract 

 when the cell is turgid. An English writer has recently sug- 

 gested the term " water-absorbing power of the cell " for this 

 quantity (Thoday, " On Turgescence and the Absorption of 

 Water by the Cells of Plants," New Phyt., 17, 108-113, 1918), 

 but this loose use of the term " power " for a quantity which 

 is undoubtedly a pressure is to be deprecated. 



Ursprung and Blum describe two methods for measuring the 

 suction pressure of cells, the simpler of which, and the one which 

 is likely to come into general use, consists in determining 

 the concentration of sucrose in which the cell neither loses nor 

 gains in volume. The osmotic pressure of this solution is equal 

 to the suction pressure. 



In a series of determinations of the suction pressures of 

 cells in the beech, Ursprung and Blum obtained definite evidence 

 of a gradient in the suction pressure in proceeding from lower 

 to higher levels. Later their observations were extended to 

 other plants (" Zur Kenntnis der Saugkraft, \\.," Ber. deut. bot. 

 Ges., 36, 577-599, 191 8), as, for example, the ivy, in which they 

 showed that the suction pressure increases with the distance 

 from the absorbing zone of the root in any particular tissue, 

 while in a cross section through any particular organ the suction 

 pressure increases with distance from the water-conducting 

 tissue. These facts are very significant from the point of view 

 of the translocation of water through plants. The only excep- 

 tion to the rule was found in the absorbing region of the 

 root, where the suction pressure is greater in the cortex than in 

 the piliferous layer ; this is to be expected. 



In their latest paper (" Zur Kenntnis der Saugkraft, IV., 

 Die Absorptionszone der Wurzel. Der Endodermissprung," 

 Ber. deut. hot. Ges., 39, 70-79, 1921) the same writers discuss 

 in particular the absorbing zone of the root. They find in this 

 organ in the broad and runner bean that the suction pressure 

 increases from the piliferous layer inwards as far as the layer 

 of the cortex next within the endodermis, but that the suction 

 pressure falls very considerably in the latter layer itself, the 

 pressure of the cells within the endodermis being even less. 

 This is very difficult to explain, the explanation offered by 

 Ursprung and Blum being that the suction pressure varies at 

 different parts of the surface of the same endodermal cell, so 

 that it is high on the side towards the cortex, but low on the 

 side towards the pericycle. In this way the endodermis acts 



