Ch. Ill, 7] 



ADJUSTMENTS TO LIGHT 



55 



a great many physiologically advantageous adjustments 

 which individual leaves, stems, roots, flowers, and other 

 organs of plants make not only toward light, but towards 

 gravitation, moisture, chemical substances, and other ex- 

 ternal influences. This very important property of respond- 

 ing thus to external stimuli is called irritability (page 39). 



Fig. 25. — A Fuchsia grown for a week in a box open only on one side ; 

 seen in profile and face view ; X i- Traced from photographs. 



Though it often simulates intelligent action, for which it is 

 sometimes mistaken by the beginner in these studies, it has 

 really no direct relation to the consciousness of animals. 

 It does, however, correspond closely with the reflex action 

 of animal physiology, each irritable, like each reflex, reaction 

 being perfectly specific and invariable in a given part to a 

 given stimulus. Being thus, in any given case, automatic, 

 these responses are properly describable as self-adjustments. 



