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 be 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. 
10 Shive, J. W., A study of physiological balance in nutrient media, 
Physiological Researches 1 (1913-1916) 327-397. 
11 Brown, W. H., The relation of the substratum to the growth of Elodea, 
Philip. Joum. Sci. 8 (1913) Bot. 1-20. 
