FACTORS AFFECTING PLANT DISTRIBUTION 16 



stages at a distance from one another. It is this careful factorial 

 analysis of the progressive changes in the vegetation which has 

 been the key to the modern ecologist's ability to get ahead. 



Succession, then, is only a phase of ecology, but a most impor- 

 tant phase. In order to have a clear notion of the relation succes- 

 sion bears to the general subject of ecology, a brief review of the 

 subdivision of the general subject seems in order. 



The Orientation of the Field of Ecology 



Ecology falls quite naturally into two principal subdivisions, 

 depending upon whether the plant responses to be studied are of in- 

 dividual plants or of groups of plants. This division separates 

 ecology into a section which is related closely to plant physiology 

 and a section related to plant geography, or into individual and 

 associational ecology. Following the names suggested by Schroeter, 

 these are called autecology and synecology. 



A. Autecology 



Autecology is the study of the responses of an individual plant 

 to its environment. It considers the general results of the plant 

 processes with respect to the life of a single plant. This is purely 

 a physiological study ; when carried on out of doors it becomes eco- 

 logical. Autecology represents to a certain extent a reaction from 

 studies which are of a laboratory nature purely. Nevertheless it 

 is in close relation to physiology which has put plant geography 

 into its proper place among sciences. On any other than a physio- 

 logical basis, plant geography is what it was in the past, pure em- 

 piricism. The study of the processes and the factors which deter- 

 mine the activities of an individual plant may be subdivided in 

 many different ways. A convenient way is to consider: (1) the 

 factors relating to changes in the growth activities of plants, (2) 

 the factors usually a part of the sequence of changes called "ad- 

 justments." 



Changes in the growth activity of plants are measured by 

 computing variations in the water loss, variations in amount of 

 carbon absorbed and in the total mineral absorption. The work in 

 this field is of such magnitude that only the least mention of it 

 may be made here. The influence of water, light, salts, and their 

 concentrations must all be investigated and the results integrated. 

 As the experimental field is opened more extensively the many ad- 



