Iheory itself, by the way in which it was deduced, gives 

 lise to the supposition, that it will not prove applicable 

 to ail cases. The theoretical reasons for which this could 

 be anticipated arc the facts mentioned above under ]o 

 and 20. In the case of purely chemical reactions van 

 't Hoffs law does not always give the expression of the 

 change of the reaction-velocity (and van I ter son adds 

 some very good instances of this fact), and in the second 

 place, the living organism differs widely from a homoge- 

 neous System, 



Thèse exceptions are by no means sufficient to make 

 Blackman's theory v^orthless. Nor is the fact, that two 

 cases are found, to which Blackman's theory docs not 

 apply, sufficient to conclude that this theory has to be 

 rejected. The less so, as in ail other processes hitherto 

 investigated, it has proved to be a valuable means of 

 reaching a better understanding of the origin of the opti- 

 mum-curve. 



§ 16. Summary of results. 



Summarising this investigation we can say, that Black- 

 man's theory is applicable to the influence of température 

 on the presentation-time in geotropism in the case of 

 coleoptiles of Avena sattca, provided that the favourable 

 influence of high températures as a time-function is taken 

 into account. 



Van 't Hoffs law holds good in the case hère investi- 

 gated between 5^ G, and 30» C; the coefficient for 10» C. 

 rise of température is 2.6. 



Between 0° C. and 25° C. the same presentation-time is found 

 after 1 hours' and after several hours' preliminary warming. 



At 30» C. the influence of the duration of the prelimi- 

 nary warming is very clearly seen. During the first hour 



