3 



grown in that soil will be the smallest of 

 the fractions a/a, h/jB, c/y, d/h, e/c, f/t„ 

 g/f]. In this case a, ^, y, etc., may be called 

 specific growth values for the plant under 

 consideration. When the available amounts 

 of the essential inorganic food constituents 

 are divided by their respective growth 

 values, the smallest quantity obtained gives 

 the maximum amount of growth possible. 



It was in this connection that Liebig^ first 

 formulated the Law of the Minimum which, 

 as commonly stated,* says that "the yield 

 of any crop always depends on that nutri- 

 tive constituent which is present in mini- 

 mum amount." The use of the term mini- 

 mum is not strictly accurate, as can be seen 

 from the example of KOH and HCl. If 

 three grams of each are present, the amount 

 of KOH determines the yield of KCl, al- 

 though both HCl and KOH are present in 

 equal amount. However, the above state- 

 ment of the law is convenient because of its 

 simplicity. 



A much broader application of the Law 

 of the Minimum was indicated by the work 

 of F. F. Blackman, whose conclusions are 

 summarized in his paper on "Optima and 

 limiting factors."^ Blackman called atten- 

 tion to the complexity of the process of car- 

 bon assimilation, the rate of which depends 

 on at least six factors — 



1. Temperature, 



2. Light intensity, 



3. Carbon-dioxide supply, 



4. Water supply, 



3 "Die Chemie in ihre Anwendung auf Agricul- 

 tur und Physiologie, " 7'« Auflage, 2: 225, 1862. 



iCf. F. Czapek, "Biochemie der Pflanzen," 2: 

 841, 1905. 



6 Annals of Botany, 19 : 281-295, 1905. 



