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PREFACE 



Parts I and II of this volume consist of an essay for 

 -hich the Cartwright Prize was awarded by the College 

 f Physicians and Surgeons of Columbia University in 

 909. The entire volume is the outgrowth of an intensive 

 and extensive study of the processes of orientation in plants 

 and animals, especially those without eyes, i.e., a study of 

 he perplexing and interesting question as to how these or- 

 canisms regulate their activities so as to bend or move 

 oward or from the source of stimulation. But while the 

 >ook deals primarily with the question of orientation, it 

 las a broader aspect and may be considered a treatise on 

 the behavior of organisms based on their reactions to light, 

 'he generality of the treatment of the subject of actions 

 1 organisms, including plants as well as animals, it is hoped 

 all make the work of value to all students of nature, espe- 

 cially to those interested in comparative psychology, 

 zoology, botany and physiology. 



Throughout the work it has been my aim first of all to 

 tate precisely what organisms do under different condi- 

 tions of illumination, and then to consider the bearing of 

 the observed reactions on the various theories that have 

 been formulated regarding reactions in general. This aim 

 has made it necessary to present somewhat lengthy and 

 detailed descriptions of methods of stimulation and re- 

 sponses which, it is feared, may be rather tedious to those 

 who are interested only in the general aspect of the problem. 

 To such it will be of particular advantage to consult freely 

 the table of contents and the summaries. 



The historical chapters which are found in Part I deal 

 with the origin and development of theories regarding 

 the activities of organisms, especially those associated with 

 light. No attempt has been made in these chapters to 



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