PREFACE. XI 



interpreted by an imagination of unrivaled vigor. It was charac- 

 teristic of this epoch that chief stress was laid upon the Hving environ- 

 ment, or "biological factors," while little or no attention was given 

 to the fundamental physical factors. Much careful work was done 

 relative to the importance of insects for pollination — the structures 

 in plants which serve to attract insects of a beneficial character or to 

 repel harmful insects, mammals, snails, or toads. It is impossible, 

 however, to overestimate the value of this period, in which travel and 

 outdoor observation received such a great stimulus. Many facts were 

 assembled, and the value of these was by no means vitiated through 

 the frequently wrong interpretations that were placed upon them. 



The rapidly approaching completion of our knowledge of the floraa 

 of the world, and the inevitable slowness of all further investigations 

 as to their origin and geologic history, have led to a great growth of 

 interest in the natural assemblages of plants — in those plant communi- 

 ties, large and small, which we designate as vegetation. For 25 years 

 there has been an increasing interest in the study of vegetation. This 

 has been partly an outgrowth of the relatively finished condition of 

 the science of floristics and partly a result of the readjustment of the 

 principles of the interrelation of the plant and its environment. The 

 study of vegetation has already passed through the descriptive phase 

 which ushers in every new branch of science, into its period of greatest 

 fruitfulness, and has brought its leading problems to the point at which 

 they demand for their solution a precise knowledge of the functional 

 activities of the plant and an equally precise knowledge of the environ- 

 ment. The subject of plant distribution and that of the relation of the 

 plant to its environment are inseparable, and the study of vegetation 

 during the past 20 years has been marked by a rapid coalescence of 

 these two fields. In short, the old field of plant geography and the 

 post-Darwinian field of environmental study have been brought 

 together, and have pushed their problems to a point at which physio- 

 logical facts and methods are of first importance for the next steps in 

 their solution. The modern study of plant ecology may be looked 

 upon as plant geography which has drawn its major outlines and has 

 begun to give attention to details, or it may be regarded as a study of 

 the relation of plant and environment in which the plant is viewed as 

 a functioning organism and the environment as a physical complex. 



The study of the environmental control of the activities of a single 

 species of plant has many differences from the study of the control 

 of a plant population, in so far as concerns the more general features 

 of the controls in each case, but in final analysis the two problems 

 merge into each other. It is precisely this fact that has come to be 

 generally recognized and has resulted in the coalescence that has been 

 alluded to as forming the subject-matter of ecology. 



