ABSORPTION OF CARBON 49 



the law of limiting factors may be formulated as follows: The 

 rate or intensity of any physiological process is determined, in 

 the first place, by the magnitude of that factor of all the external 

 factors, which is at a minimum. In other words, this factor being 

 in the minimum limits the influence of all other external factors. 



The law of limiting factors, representing a further development 

 of the law of the minimum established by Liebig through studies 

 of the mineral nutrition of plants, is one of the most important 

 laws determining the relation of the plant as a whole, as well as 

 of its separate physiological processes, to the external environ- 

 ment. Formerly, it was supposed that the external factors acted 

 separately. If one of them be limiting, an increase of the other 

 factors will not be able to intensify a certain physiological process. 

 Recently, however, it has been established (Benecke, Lundegardh, 

 and Harder) that the controlling influence of the minimal factor 

 is not absolute but only a relative one. It slows down but does 

 not entirely check the favorable influence of the remaining factors. 

 This relationship is represented graphically in Fig. 21, showing 

 the dependence of assimilation on the varying intensities of two 

 factors — light and of carbon-dioxide content — in the aquatic 

 moss, Fontinalis. 



