LAWS OF ENVIRONMENTAL CHANGE 83 



or of a physiological training in a psychologist. 

 For one who is ignorant of the principles of "orderly 

 sequence," or successions of changes occurring in the 

 physical, vegetational, and animal environments, 

 it is manifestly impossible to realize their develop- 

 ment ; and the application of such principles to the 

 interpretation of practical problems is utterly beyond 

 his grasp. We are thus able to see that although the 

 phrase "orderly sequence of external nature" is 

 fundamentally a simple conception, it is not grasped 

 without effort, training, and careful investiga- 

 tion. 



Obviously it is impossible to arrange the series of 

 references with perfect satisfaction. T$he arrange- 

 ment which will serve one purpose will not another, 

 and for this reason it has been necessary to arrange 

 the lists in more than one order. Certain general 

 references, or some intended to facilitate the acquire- 

 ment of the general point of view, are given first, and 

 others are arranged alphabetically. For example, 

 the papers listed on the processes of change in the 

 physical and vegetational environment are approxi- 

 mately in an order in which they may profitably be 

 studied to make the view as concrete as possible. 

 It is primarily not the abstract idea of the principle 

 of change, which is relatively easy to grasp, but to 

 be able to apply it to any condition or location and 

 to make it a guiding principle is very difficult. And 

 judging from my own observation upon others and 

 my own experience this method is very rarely mas- 

 tered, if at all, unless it is actually worked out in 



