THE TROPISMS IN GENERAL 19 



Loeb through his work "Der Heliotropismus der Tiere" and 

 various later papers. The "Heliotropismus der Tiere" 

 was a pioneer work; but perhaps its chief value lies not so 

 much in the number of interesting facts and records of 

 ingenious experiments it contains as in the general theory 

 there advanced, which has been the means of stimulating 

 many investigators to enter the field. 



The book emphasized the idea that it is the business of 

 the investigator not merely to describe the facts of behavior 

 and marvel over their wonderful nature, but to try to ex- 

 plain them. It presented him with a theory which it true 

 would carry us a step forward in the analysis of many 

 kinds of behavior, especially in the lower organisms. The 

 book shows the influence of Sachs, whose conception of the 

 mechanism of tropisms in plants forms the nucleus of Loeb's 

 theory. Loeb attempted to show that the phenomena of 

 Heliotropism were essentially similar in plants and animals. 

 The orientation of the body to the direction of the rays, the 

 fact that the more refrangible rays are the more effective in 

 producing the heliotropic response, and the dependence of 

 light reactions upon light intensity and temperature are 

 shown by plants and animals in much the same way. All 

 of these effects are supposed to rest upon certain funda- 

 mental properties of living substance common to plants and 

 animals. This conclusion was naturally a somewhat start- 

 ling one, especially when the light reactions of highly de- 

 veloped animals which were commonly supposed to be due to 

 psychic causes were placed in the same category with the 

 turning of leaves and stems toward the sunlight. 



The prospect of finding a mechanical explanation of the 

 behavior of organisms is always an alluring one. In 

 this case it proved to be especially so because the general- 

 ization included such apparently diverse phenomena, and 



