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THE AMEBIC AN NATURALIST [Vol. XLIV 



obscured by clouds, the dandelion heads are soon folded 

 together by the straightening up of the involucral bracts. 

 Xo other changes are visible, though others may be de- 

 tected by appropriate means. 



Again, external agents may act on only a limited region 

 of the plant, in which case the obvious effects may be re- 

 stricted to some special part, either that immediately 

 acted upon or one at a greater or less distance from it. 

 Thus if the cotyledon alone of a Panicum seedling be 

 lighted from one side, the hypocotyl, 20 mm. or more 

 away, instead of continuing its equal growth, may curve 

 abruptly. 



In these two cases of limited visible change, the phe- 

 nomena are explained by asserting that the protoplasm 

 is irritable and responds to an external change called a 

 stimulus. In fact, there is an inclination, after endowing 

 the protoplasm with such " properties" as " irritabil- 

 ity," "automaticity" and "self-regulation," to be satis- 

 fied with the words and there make an end. Such a tend- 

 ency, wide-spread in the prescientific days, undoubtedly 

 springs from the wonder with which one confronts an 

 uncomprehended intricate mechanism. It finds expres- 

 sion, for example, in a common saying about this or that 

 industrial machine: "It seems to have almost human in- 

 telligence." Of course no one supposes the machine 

 really endowed with other than physical qualities, oper- 

 ating through the matter and the energy with which it 

 is supplied. Yet the vitalism, which dominated the 

 earlier years of physiology, even yet controls our speech 

 and our thinking, and indeed latelv shows signs of re- 

 vival. 



Vitalism, assuming living matter to be endowed w T ith 

 special powers, called vital in distinction from physical, 

 is itself in part an expression of helplessness in the face 

 of an uncomprohonded mechanism, the living body, and 

 in part an interpretation of nature in terms of our own 

 consciousness. To seek explanation in that direction is 

 to proceed from the simple to the complex; but the ex- 

 planation of phenomena must be a process of analysis. 



