INFLUENCE OF TEMPERATURE 



25 



In consequence of these divergent results, Bolus and Hen- 

 derson * have undertaken a critical investigation of the subject 

 in laboratory conditions, and in their preliminary communi- 

 cation they report that the enrichment of the air with carbon 

 dioxide results in a large increase in the dry weight of plants 

 of Cucumis sativa as compared with the plants grown in 

 normal air, which increase is evident within two or three days 

 from the beginning of the experiment. The following table 

 summarizes their results : — 



TEMPERATURE. 



The statement that chemical change is profoundly in- 

 fluenced by temperature needs no elaboration : in the majority 

 of instances an increased temperature accelerates a reaction ; 

 examples in which the contrary occurs are very few. The Law 

 of van't Hoff states that for every rise in temperature of io° C. 

 the reaction is increased at a definite rate, in general terms 

 doubled or trebled, the precise value of which is specific to the 

 reaction, f The plant, however, is not a test tube but a very 

 complex system of reacting substances, wherefore it is only in 

 experiments most carefully controlled. and skilfully conducted 

 that approaches to the mathematical preciseness of well- 

 ascertained physico-chemical laws will obtain. 



Long has it been known that an increased temperature 

 results in an increased carbon assimilation, but it was not 



* Bolus and Henderson : " Ann. Bot.," 1928, 42, 509. 



| This factor is termed the temperature coefficient and is represented 

 by the symbol K with a number attached indicating the number of degrees 

 concerned, e.g. K 10 . 



