No. 575] RESPONSES OF PLANTS AND ANIMALS 



1. Kesponses 



The word response is used in various slightly different 

 senses. In general it refers to more complex and time- 

 requiring phenomena than ' 1 reaction. ' ' In geography the 

 term has been used (G-oode, '04) to cover all changes in 

 culture supposed to be produced by climate or other 

 geographic conditions. It is also applied by geographers 

 and geologists to changes in the physical characteristics 

 of man (evolution) which Goode ('04) has stated are 

 slower than the cultural responses. In general botanists 

 have used the term to cover changes of plant structure 

 and function induced by external conditions. Cowles 

 ('11), however, uses the word "reaction" to cover these 

 phenomena. Coulter ('09) used the term response as 

 synonymous with adaptation in plants. Zoologists have 

 used the term to apply to changes in animals due to exter- 

 nal conditions, but with little agreement as to what is to 

 be included. We will use it here to include reactions, 

 changes in functions, structure, color, induced by external 

 conditions either directly or indirectly, without regard 

 to how simple or how complex the processes involved 

 may be. 1 The length of time required to bring the 

 changes about may arbitrarily be taken as not exceeding 

 the time required to breed five to ten generations of the 

 species concerned. All organisms respond to stimuli 

 because each stimulus acts upon some internal process. 

 Strictly speaking, the response is the change or changes 

 in the physical or chemical processes of the organism {or 

 the part or parts concerned) which results from the 

 disturbance. 



Those things which we commonly see and term response 

 are often the later and less important phases of the dis- 

 turbance. The striking phases of responses of motile 

 organisms are usually movements which follow closely 

 upon stimulation. In sessile organisms the noticeable 

 responses often appear only after a considerable period. 

 In both sessile and motile organisms some responses are 



1 For good representative bibliography Bee Adantt, '13, Ch. VIII and 



