15 



In this way the condition of the root sys- 

 tem affects the leaves and the condition of 

 the leaves affects the root system. Correla- 

 tions are therefore manifestations of the 

 principle of integration. 



The organic world can be analyzed into 

 systems of various orders, those of a higher 

 order being inclusive of, or divisible into, 

 systems of a lower order. These systems 

 are invariably overcoming the effects of 

 limiting factors. The limiting factor is the 

 stimulus to which the system reacts. The 

 reaction places the organism in a more effi- 

 cient relation with its environment, but no 

 matter how many reactions are carried out, 

 there is always some limiting factor left, 

 and so the organism is kept constantly 

 busy. The end result is to approximate 

 more or less closely some kind of average 

 of all the resources at its disposal. 



I think it might be possible to go even 

 further and get a quantitative measure of 

 the degree to which the process of integra- 

 tion has been carried, by considering the 

 number of factors integrated and how close 

 an approximation to the normal curve of 

 error had been obtained. Such a quantita- 

 tive measure would likewise be an index of 

 the stage of evolution that an organism had 

 reached." At the very least, the Law of 

 the Minimum or the principle of limiting 

 factors offers a sound basis from which such 

 intangible processes as behavior, correla- 

 tions, evolution and ecological succession^® 

 1* Our criterion of ' ' degeneracy " in a living or- 

 ganism is based essentially on a decrease in the 

 number or range of factors between which inte- 

 gration is possible. 



15 For an application of the principles enunci- 

 ated in this paper to plant ecology see G. E, Nich- 

 ols, Plant World, Sept., 1917. 



