PART I 



PLANT SUCCESSIONS 



The study of plant succession is an analysis of the develop- 

 mental process of vegetation. It is a recognition of the causes of 

 plant distribution. The tracing of the development and the study 

 of the causes have always gone hand in hand. The former leads 

 finally to the classification of vegetation on an ecological basis, the 

 latter to experimental physiology. 



The broad concepts of plant distribution formulated from 

 time to time may be regarded as steps in the progress of ecological 

 development, each step bringing one closer to the complete classifi- 

 cation. Discovering the causes of plant succession involves changes 

 in methods of study, but does not necessarily alter the concepts. 



The advance of the study of the causes of plant distribution 

 depends upon progress in the invention of new instruments, and 

 better ways of operating the existing ones, to measure the plant 

 environment ; that these two ways of examining plant distribution 

 have always been employed by the ecologists who have contributed 

 most toward the advance of the science is apparent from the liter- 

 ature. It is quite likely that these two methods will always be used 

 together. 



Plant succession represents our most advanced trend of 

 thought in ecology. In its simplest form ecology is the observation 

 of plants and animals in relation to their surroundings and to one 

 another. The genesis of the vegetation from bare areas to highly 

 developed associations of plants is the basis of the examination of 

 successions. Ecologists taking advantage of the point of view of 

 successions are able to use shorthand methods for studying the 

 plants in the field. They thus make descriptions which are con- 

 cise as well as complete. By using shorthand descriptions of field 

 conditions and measuring these conditions carefully with the vari- 

 ous instruments designed for the purpose, the ecologist takes his 

 laboratory out into the field with him. 



In most sciences, as time goes on, a broad generalization gives 

 way to one that is still broader, still more daring, more inclusive. 



13 



