ADAPTATION 169 



to the study of plants. There exist very many external 

 formative stimuli in the morphogenesis of vegetation : 

 would it then be possible to regard every effect of such 

 an external formative stimulus as a real morphological 

 adaptation ? No ; for that would not meet the point. 

 The general harmony of form is indeed concerned if gravity 

 forces roots to shoot forth below at a spot where they can 

 enter the ground, or if light induces branches and leaves 

 to originate at places where they can obtain it for assimila- 

 tion ; but gravity and light themselves are mere formative 

 stimuli of the localising type in these instances, for 

 they relate only to the individual production of form, not 

 to the functioning of already existing form. We therefore 

 are warned not to confuse the effects of formative stimuli 

 from without with real adaptive effects until we have fully 

 analysed the particular case. 



We have drawn a sharp line between causes and means 

 of morphogenesis, applying the term " means " to those con- 

 ditions of the morphogenetic process which relate neither to 

 the specificity nor to the localisation of its constituents, 

 though they are necessary for the accomplishment of the pro- 

 cess in the most thorough manner. Would it be possible to 

 connect our new concept of an adaptation with our well- 

 established concept of a means of morphogenesis in such a 

 way that we might speak of a morphological " adaptation ' 

 whenever any specific feature about morphogenesis proves 

 to be immediately dependent for its success on some specific 

 means, though it does not owe its localisation to that means 

 as its " cause " ? It seems to me that such a view would 

 also fall wide of the mark. It is well known, for instance, 

 that the flowers of many plants never fully develop in the 



