No. 575] RESPONSES OF PLANTS AND ANIMALS 657 



etc., and biological (due to organisms). Sessile plants 

 are the chief biological cause of succession on land and 

 in fresh water, while sessile animals are the chief biolog- 

 ical cause in the shallow portions of the sea, especially in 

 coral reef regions (Wood- Jones, '11). Sessile organisms 

 are more important causes of succession than motile ones 

 because they (a) build up the substratum with detritus 

 and skeletons, (b) interfere with the movement of the 

 surrounding medium, (c) cut off light from the sub- 

 stratum where other organisms must reside and their 

 own young secure foothold, and (d) they usually affect 

 their own environments with excretory products more 

 than do motile organisms. In general we recognize 

 ecological succession of motile animals through the differ- 

 ences of behavior which accompany changes in conditions. 

 The differences are physiological ; differences in behavior 

 are the easiest index of the physiological condition. The 

 character of nests, burrows, etc., are often good indi- 

 cators also. 



IV. INFLUENCE OF RESPONSE PHENOMENA UPON BIOLOGICAL 

 THEORY AND CONTROVERSY 



A glance at some aspects of biological speculation 

 since before the publication of Darwin's " Origin of 

 Species" is essential to our understanding of the atti- 

 tude of biologists until recently, toward responses. 



1. Teleological View 

 In the matter of animal behavior response, the earlier 

 workers interpreted the reactions as intelligent and pur- 

 poseful, ascribing human sensations, etc., to animals as 

 low in the scale as protozoa. This teleological tendency 

 was paralleled on the plant side by the idea of purposeful 

 adaptive responses. Many common plants respond 

 (structurally) readilv to environmental conditions. As 

 has been noted, the commonest of the surviving responses 

 of the wild state are apparently advantageous. This led 

 some botanists to a Lamarckian teleological conception of 

 response, perhaps best represented by Kerner and 



