350 The Philippine Journal of Science 



his early illustrations from simple chemical and physical processes, for 

 it is rapidly becoming a question whether the law applies to plant activities 

 as generally as or with anything like the rigidity assumed by some 

 workers. The fact of vicarious conditions, or stimuli, renders the concep- 

 tion of limiting factors less definite. In some light requiring seeds, for 

 instance, several things can be substituted for light, as salts, higher 

 temperatures, acids, etc. To speak of the lack of sufficient light as a 

 limiting factor to germination helps little. What should be learned is, 

 what internal condition, or inhibitor, may any one of these factors act 

 upon to initiate growth? The conception of an external condition as a 

 limiting factor frequently leads physiologists to fail to examine the internal 

 mechanism upon which that and other factors play to bring about a 

 given result. The reviewer feels that the law of the minimum should 

 be applied to biological problems with due realization of its limitations. 



Examples might be easily multiplied. Shive, 10 working with 

 three salt solutions found that, for a given set of external 

 conditions and a given total concentration, there was a certain 

 set of salt proportions that gave the best growth. For another 

 total concentration, however, all the other conditions remain- 

 ing as before, quite another set of salt proportions was most 

 favorable for growth// It is difficult to see how the theory of 

 limiting factors could^e applied to such a case. Brown, 11 work- 

 ing with Elodea in tap water, found that either an increase 

 in the carbon-dioxide supply or the addition of nutritive salts 

 produced an increased rate of growth. 



The law of the minimum seems to be applicable within limits 

 when dealing with quantities of reacting chemicals which pro- 

 duce a given substance; but the law of the minimum, or the 

 theory of limiting factors, certainly does not appear to apply 

 generally to physiological processes, or even to chemical phe- 

 nomena with regard to combinations of such factors as tem- 

 perature, pressure, and concentrations. 



" Shive, J. W., A study of physiological balance in nutrient media, 

 Physiological Researches 1 (1913-1916) 327-397. 



" Brown, W. H., The relation of the substratum to the growth of Elodea, 

 Philip. Journ. Sci. 8 (1913) Bot. 1-20. 



