LAWS OF VARIATION 207 



acters. Hence modifications of structure, viewed by sys- 

 tematists as of high value, may be wholly due to the 

 laws of variation and correlation, without being, as far 

 as we can judge, of the slightest service to the species. 

 We may often falsely attribute to correlated variation 

 structures which are common to whole groups of species, 

 and which in truth are simply due to inheritance; for 

 an ancient progenitor may have acquired through natural 

 selection some one modification in structure, and, after 

 thousands of generations, some other and independent 

 modification; and these two modifications, having been 

 transmitted to a whole group of descendants with diverse 

 habits, would naturally be thought to be in some neces 

 sary manner correlated. Some other correlations are ap- 

 parently due to the manner in which natural selection 

 can alone act. For instance, Alph. de Candolle hay 

 remarked that winged seeds are never found in fruits 

 which do not open; I should explain this rule by the 

 impossibility of seeds gradually becoming winged through 

 natural selection, unless the capsules were open; for in 

 this case alone could the seeds, which were a little better 

 adapted to be wafted by the wind, gain an advantage 

 over others less well fitted for wide dispersal. 



Compensation and Economy of Growth 



The elder Geoffroy and Goethe propounded, at about 

 the same time, their law of compensation or balancement 

 of growth; or, as Goethe expressed it, "in order to spend 

 on one side, nature is forced to economize on the other 

 side." I think this holds true to a certain extent with 

 our domestic productions: if nourishment flows to one 

 part or organ in excess, it rarely flows, at least in ex- 



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