as starting-point. At 30° C. e. g. the values C, — Cj found 

 after 1 — 4 hours are plotted as beginning vvith the ordi- 

 nate oî 30° C. as starting-point, while afterwards the 

 curve drawn through thèse points C» — Cs Is continued 

 backwards to Ci. 



Now Black m an holds that the first experimentally 

 found value for a given high température must already 

 be toc low; it is the value after one hour and we must 

 hâve the value after a time zéro. By extrapolation from 

 the curve drawn through the points representing the 

 values after one to four hours he gets the values for the 

 time zéro. This value must be identical with what he 

 gets by calculating according to van 't Hoffs law. In 

 the assimilation-diagram this indeed cornes out fairly 

 well, but the extrapolation from the time-curve may hâve 

 been made somewhat arbitrarily. 



Black m an comes to the conclusion that in many if 

 not in ail cases van 't Hoffs law would be found appli- 

 cable to physiological processes and the optimum would 

 vanish, if déterminations could be carried out after war- 

 ming during a time zéro. At présent the initial values 

 are only to be found by extrapolation and calculation. 

 The second part of Blackman's paper deals with ,,limi- 

 ting factors." 



When the rate of a process dépends on a number of 

 separate factors, the rate is limited by that of the slowest 

 factor. This is virtually the same as .,the law of the 

 minimum", but its application to physiological reactions 

 has mostly been overlooked. 



Considering the case of assimilation we can recognise 

 five factors which can control the reaction-velocity: the 

 amount of CO2 available, the intensity of available radiant 

 energy, the amount of HiO available, the amount of chlo- 

 rophyl présent and the température. If in investigating 



