69 



In this case the action of the enzyme might be the 

 process in question, or the formation of the enzyme, as 

 the perception would proceed faster if the quantity of the 

 enzyme were greater. 



Thèse considérations are only given hère to point ont 

 clearly that geotropic perception is not necessarily a 

 simple Chemical process, but merely that van 't Hoff's 

 law is applicable to the presentation-time; this one fact 

 alone does not make it possible to dravv conclusions about 

 the nature of perception. 



In summarising we can sây that vvith respect to van 

 't Hoffs law Blackman's theory is confirmed by this 

 investigation. Just as Miss Matthaei found in the case 

 of assimilation, and Kuyper in the case of respiration, 

 so hère too the reaction-velocity at average températures 

 increases at the same rate for every 10° C. rise of tem- 

 pérature. The température-coefficient is 2.6. 



The paper by van Iterson and Miss van Amstel. 

 who concluded from their experiments that Blackman's 

 theory must be rejected, will be discussed separately in ^ 15. 



§ 13. Optimum and time-factor. 



One of the cardinal points in Blackman's paper is 

 the theory that the optimum is not the expression of a 

 primary gênerai relation between température and a 

 physiological process, but varies vvith the time of observa- 

 tion. Closely connected with this is the fact (supposed to 

 be of much importance by Black m an), that at highei" 

 and harmful températures the intensity of a physiological 

 process' decreases in subséquent hours, which falling off 

 is strongest in the first hours of a stay, at a given high 

 température. I recall the way in which Blackman 

 thoughi it possible to reach the theoretical initial value 



