282 CHAP. XXVIII. GENERAL REVIEW 



new classes of phenomena, instances of which are found in 

 the prolongation of the Induction-period under increasing 

 duration of darkness, and of photosynthetic efficiency higher 

 than normal under rapidly intermittent light. The nature 

 of the change of activity under variation of one factor at a 

 time has been ascertained from the characteristics of the 

 photosynthetic curve. The adoption of the absolute scale 

 in physiological measurements has led to the establishment 

 of a simple law of photosynthesis. In nature the photo- 

 synthetic organ is acted on not by one but by many changing 

 factors, the resultant effects of the simultaneous variation 

 of which are innumerable. It is the high complexity 

 introduced by the many possible combinations of the 

 constituent factors which renders the analysis of life-pro- 

 cesses so extremely difficult. An analogous case in physics 

 will give some idea of the difficulties involved. Before the 

 discovery of the law of dilatation of gases the changing 

 volume of a gas under variation of pressure and temperature 

 must have caused great perplexity. It was the establish- 



py 



ment of the law that -=- is a constant that led to very 



important advances in physics ; in chemistry not even an 

 elementary advance would have been possible without the 

 application of this law. 



The comp'icating factors in photosynthesis are far more 

 numerous ; it is hoped that the introduction of measurement 

 on the physiological scale and the establishment of the 

 Law of Product will lead to as great an advance in Plant 

 Physiology as the introduction of absolute measurement 

 has accomplished in Physical Science. 



