No. 502] CHEMICAL MECHANICS IN LIVING PLANT 661 



I am not acquainted with any data for the growth rate 

 of whole flowering plants at different temperatures : Of 

 course the case of growth most usually measured in the 

 laboratory, namely, where one part of a plant extends 

 at the expense of the reserves stored in another part and 

 there is a decrease, not an increase, of total dry weight, 

 is not the type of growth we have to deal with. Even 

 for simple elongation of a shoot at different temperatures 

 we have but few data. Those of Koppen (1870) gener- 

 ally quoted are wildly irregular, and in many cases it is 

 clear that the growth-extension of complex structures is 

 a process which proceeds by spasms rather than smoothly. 



The rate of movement of circulating protoplasm in- 

 creases rapidly with temperature, but Velten's numbers 

 do not give an obvious logarithmic curve. If we con- 

 fine our attention to the values for 29° C. and 9° C. we 

 do find, however, that the velocity increases about two- 

 fold for each rise of 10° C. being 10 mm. at 9° C. and 

 40 mm. at 29° C. 



Taken altogether these various data clearly support 

 the hypothesis that temperature accelerates vital proc- 

 esses in the same way as it does non-vital chemical re- 

 actions, that is, logarithmically by an approximately con- 

 stant factor for each rise of 10° C. ; and, further, it ac- 

 celerates them to the same extent; that is, that the factor 

 in question has values clustering about 2-3. 19 



To make these similarities more significant I ought to 

 point out that no other properties of matter are acceler- 

 ated to anything like this extent by rise of temperature. 

 Most reactions increase in velocity by no less than 10 per 

 cent, per degree rise of temperature; a most marked 

 effect, and yet there is no generally accepted explanation 

 of this almost universal phenomenon. By the kinetic 

 theory of gases each rise of a degree in temperature in- 

 creases the movements of the gas-molecules, so that the 



