6 



carbon assimilation — the water supply, 

 chlorophyll and enzymes. These so-called 

 "internal" factors, as well as the "exter- 

 nal" factors, are governed by the Law of 

 the Minimum. Of the internal factors, 

 water and chlorophyll are present in ex- 

 cess in healthy green plants, the amount of 

 assimilatory enzymes being the only prob- 

 able limiting factor. 



It is not necessary to adduce additional 

 examples to show that the Law of the Mini- 

 mum is a universal law, affecting not merely 

 the concentration of reacting substances, 

 but all factors that in any way influence a 

 reaction or process. The law is applicable 

 to physical, chemical and geological as well 

 as biological problems.'' An interesting in- 

 stance of its application to a problem in 

 physics is the determination of the magni- 

 tude of a thermionic current. This varies 

 with changes in temperature, and also with 

 changes in the voltage applied. The tem- 

 perature formula gives one value, the vol- 

 tage formula may give another; the lesser 

 value determines the current flowing. The 

 application of the Law of the Minimum 

 has been worked out in many cases and has 

 been of great use in the interpretation of 

 complicated relations ; but it has been rec- 

 ognized as a law and has been consciously 

 applied by plant physiologists and physio- 

 logical chemists only.^ Without doubt it 

 can be used to advantage in many problems 



7 A timely application may be made which is 

 worth bearing in mind. The efficiency of a nation 

 at war is subject to the Law of the Minimum. 

 Defeat, in the last analysis, may be attributed to 

 the effect of some limiting factor. 



8 Cf. the work of L. B. Mendel, T. B. Osborne 

 and their pupils. 



