Power to Adjust Parts to Surroundings 255 



power, he is chosen quite anew at regular intervals in adjustment 

 to the popular demands of the moment, only the method of elect- 

 ing him being permanent, or, so to speak hereditary; while the 

 monarch holds his office by heredity quite regardless of the 

 fluctuations of politics. As to our second question, whether in 

 the last analysis, the two may not be fundamentally the same, 

 adaptive structures being only permanently-fixed irritable ad- 

 justments, the view is attractive but as yet unproven, as we shall 

 further consider in the chapter on Evolution. 



There remains one other important matter to mention in con- 

 nection with stimuli. The response to a stimulus, while highly 

 efficient, is blindly invariable, and not alterable for particular 

 conditions. For example, if a wind-blown seed of an ordinary 

 plant were to lodge in a cleft of an overhanging ledge, it would 

 be an advantage for this plant to be able to reverse the usual 

 positions of roots and stem; yet we know it would send its stem 

 up, though only to die in the earth, and its root down, only to 

 perish in the air. In this invariability of particular responses, 

 and in many respects besides, these irritable responses of plants 

 agree with the reflex actions familiar in animals; and it is now 

 very clear that they are essentially the same. Furthermore, if 

 two or more stimuli act upon the same part of the plant at the 

 same time, the result is simply the product of the effort of the 

 part to respond to them all. There is no sign of an attempt on 

 the side of the plant to correlate these stimuli, so to speak, and 

 to respond in a manner which would be best in the face of this 

 particular combination. In this respect animals have gone far 

 ahead of plants, for they have acquired that last-mentioned 

 power. Herein we have the chief feature which distinguishes 

 the higher animals from the higher plants, and also, I believe, 

 the origin of consciousness. Thus, out of one and the same 

 origin, plants have developed irritability, while animals have 

 developed reflex action, consciousness, and ultimately reason. 



