370 



THE MAINTENANCE OF THE INDIVIDUAL 



Francis B. Sumner 



Dr. Sumner's experiments with flounders show 

 a response of the animal to different backgrounds. 

 How would you attempt to account for this .•* 



environment by chang- 

 ing their color pattern. 

 There may even be elec- 

 tric responses to stimuli 

 as seen in the discharge 

 of as much as 300 volts 

 from the electric organ of 

 the electric eel, a shock 

 sufficient to kill a horse. 

 In the higher animals 

 where well-developed or- 

 gans have been evolved, 

 an organ is usually at- 

 tuned to one kind of 

 stimulus and responds 

 only to that particular 

 stimulus. The eye, for 

 example, responds to light 

 waves, but to no other 

 ether waves, while the 

 organ of Corti in the mam- 

 malian ear distinguishes 

 with accuracy betw^een 

 different wave lengths 

 which cause sounds. Thus 

 the nature of responses 

 depends not upon the 

 stimulus, but upon the 

 kind of cells stimulated. 



Mechanisms of Response in Plants 



It is much easier to show that plants respond to stimuli than to 

 explain how they do. Most of the responsive activities of plants do 

 not, as one author puts it, result in "discriminating movement" so 

 much as in ''discriminating growth." If a growing root is photo- 

 graphed every ten or fifteen minutes and these pictures greatly 

 magnified are projected as a slow motion motion picture, the root 

 seems to act like an intelligent "white worm," pushing aside soil 

 particles, avoiding obstacles, and ultimately finding its way to an area 

 where water exists. 



