TABLE OF CONTENTS ix 



a. Random movements and avoiding reactions; b. Orienta- page 

 tion, change in sense of orientation, and avoiding re- 

 actions; c. Orientation and extent of movement limited 

 by environment; d. Orientation and movement directly 

 toward the place where the organism comes to rest; 

 e. Random movements and coming to rest in a given place. 



CHAPTER XII 



Reactions to Light which do not Result in Aggregation or 



Orientation 



1. Reactions to Shadows — Protective 247 



2. Reactions to Shadows — Procuring Food 249 



3. Reactions to Sudden Increase of Light Intensity 250 



4. Reactions to Light caused by the Effect of Continued Illumi- 



nation 252 



5. Classification of Reactions to Light — Phototropism, Pho- 



topathy . 253 



6. Reclassification of Reactions to Light 256 



(i) On the basis of the character of the stimulus. 

 a. Reactions to change of intensity; b. Reactions to con- 

 stant illumination; c. Reactions of questionable cause. 

 (2) On the basis of the fundamental causes of the response. 

 a. Reactions caused by the direct effect of light on the 

 reacting tissue; b. Reactions caused by an indirect effect 

 of light; c. Reactions due, not to any effect of light in 

 itself, but to what a given light condition or configura- 

 tion may represent. 



7. Evolution of the Reactions to Light 262 



CHAPTER XIII 



Factors Involved in Regulating Reactions to Light — Variability 



and Modifi ability in Behavior 



I. Change in Sense of Reactions 265 



a. Effect of intensity of light; b. Effect of change in tem- 

 perature — Original observations; c. Effect of chemicals 

 — Original observations; d. Effect of concentration of 

 the medium and mechanical stimuli; e. Effect of internal 

 changes. 



