LIGHT AND THE BEHAVIOR 

 OF ORGANISMS 



PART I 



INTRODUCTION AND HISTORICAL REVIEW 



CHAPTER I 

 GENERAL INTRODUCTION 



That plants and animals respond to stimulation by 

 light Is a matter of common Information. It Is also well 

 known that many of the motile forms collect In regions 

 of a given Intensity of light; that many orient, some moving 

 or turning toward a source of light, others away from It; 

 and that many go toward a source of light under certain 

 conditions and away from It under others. The distribution 

 of the power to respond to stimulation by light Ii> the plant 

 and animal world has likewise been quite fully ascertained,^ 

 and numerous accurate observations concerning the precise 

 methods of response have been recorded. There is how- 

 ever still much contention as to the explanation of these 

 phenomena, and It Is this that concerns us chiefly In this 

 work. In what manner and for what reasons do organisms 

 collect In regions of certain light Intensity? How do they 



1 See Wiesner, 1879, 1881; Verworn, i88g, pp. 35-61; Nagel, 1896; 

 Davenport, 1897, pp. 182, 195; Radl, 1903, pp. 64-67; Washburn, 1908, 

 pp. 120-147; Congdon, 1908. 



The works of these authors referred to by means of the dates following 

 each name, as well as those of all other authors similarly referred to in the 

 text, will be found in the bibliography. 



I 



