1912.] Absorption of Water by Seeds of Hordeum vulgare. 549 



Diagram II. 



The course of the lines in the diagram, in respect both of straightness and 

 agreement of inclination, furnishes evidence of a most conclusive character 

 that the rate at which water is absorbed by the barley seeds is an exponential 

 function of the temperature. 



Such a conclusion is of special interest, not only on account of the rarity of 

 an exponential increase of a physical property with rise of temperature,* but 

 more especially as the vapour pressure of water is also approximately an 

 exponential function of the temperature. 



In Diagram II the logarithms of the vapour pressure of water over the 

 range of temperature covered by the absorption experiments are plotted 

 against the temperature as a dotted line. The highly important fact is thus 



* " An exponential increase of any physical property with rise of temperature is very 

 rare. The increase of the vapour pressure of a liquid with rise of temperature is an 

 exception and, in consequence, Arrhenius concludes that the increase of the velocity of a 

 chemical reaction with temperature cannot be explained by any change in the physical 

 property of the solution with temperature." Mellor's ' Chemical Statics and Dynamics, 

 1904, p. 394. 



VOL. LXXXV. — B. 2 Q 



