72 



Hoffs law. It appears very cleaiiy from thèse figures, 

 that tho favourable influence of the température of30°C. 

 is seen only after a long preliminary warming. 



The température of 30° C. has already a harmful influ- 

 ence too, as is shown by the above figures and more 

 clearly by the curves on plate V. After one hours' war- 

 ming the presentation-time at 30° C. is S'SO" and in the 

 next hour it decreases to 2'30". Now this value 3'30" after 

 1 hour cannot be explained if we do not take into account 

 a harmful influence, which at first hindered the presen- 

 tation-time from becoming lower. It could hâve been lower 

 after 1 hour, for at 25° C. (at which no harmful influence 

 can be traced) the value after 1 hour is only 2'20". 



Summarising we find at 30° C. first a harmful influence 

 of little importance, and further a favourable influence, 

 which is a function of the time of preliminary warming, 

 and overcomes the harmful influence, so as to make the 

 presentation-time reach the theoretical value according to 

 van 't Hoffs law. 



It is not only on the ground of my own results obtai- 

 ned at 30° C. that I offer the opinion, that the favourable 

 influence of a high température needs some time to make 

 itself fully felt; in varions places in the literature on this 

 subject the same idea is to be found, and several facts 

 find an easy explanation in this way. 



As early as 1860 Sachs') wrote: „Jede Temperatur 

 wirkt auf die Vegetationsprocesse, ob sie in der Zeit der 

 Keimung oder spater fallen, nur dann, wenn sie eine 

 bestimmte Zeit hindurch anhillt". An instance is to be 

 found in Sachs' paper on the influence of température 

 on growth. ^) On plates III and IV temperature-curves are 



1) J. Sachs, 1860, p. 358. 



2) J. Sachs, 1872. 



