9 



perature acts, the more the enzyme is de- 

 composed, within certain limits. The jtudy 

 of the action of salt solutions on permea- 

 bility, growth, etc., involve even greater 

 complications produced by the interrela- 

 tion of conditioning factors. 



In order to get an accurate statement of 

 the Law of Minimum, it is necessary to 

 get away from the custom of discussing 

 causes, however difficult this may be.^^ 

 The idea of causation invariably indicates 

 incomplete analysis. A biological phenom- 

 enon is dependent not on a single variable, 

 but on a complex or constellation of factors, 

 as we have seen in the case of carbon as- 

 similation. It should be discussed there- 

 fore in terms of all the conditioning fac- 

 tors, not in terms of that one which tempo- 

 rarily happens to be a limiting factor. The 

 term "function" is valuable in this con- 

 nection. The amount of carbon assimila- 

 tion is a function of the temperature ; it is 

 another function of the illumination, etc. 

 With this idea of function in mind, the Law 

 of the Minimum may be stated in the fol- 

 lowing form. When a quantity is depend- 

 ent 071 a number of variable factors and 

 'fnust be a function of one of them, the 

 quantity is that function which gives the 

 minimum value. Expressed in plain Eng- 

 lish this means that a chain is no stronger 

 than its weakest link. The Law of the 

 Minimum is only too obvious. Its applica- 

 tion is often so self-evident that it is made 

 as a matter of course. 



But the most interesting thing about the 

 law is not how it works, but when it does 

 not work. There is a fundamental discrep- 

 ancy between the Law of the Minimum and 



11 Cf. B. E. Livingston, loc. cit. 



