158 ORIGIN OF SPECIES 



coelospermous in the central flowers, — that the elder De 

 Candolle founded his main divisions in the order on such 

 characters. Hence modifications of structure, viewed by 

 systematists 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 selec- 

 tion 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 nat- 

 urally be thought to be in some necessary manner correlated. 

 Some other correlations are apparently due to the manner 

 in which natural selection can alone act. For instance, Alph. 

 de Candolle has 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 economise 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 excess, to another part; 

 thus it is difficult to get a cow to give much milk and to fat- 

 ten readily. The same varieties of the cabbage do not yield 

 abundant and nutritious foliage and a copious supply of oil- 

 bearing seeds. When the seeds in our fruits become atro- 

 phied, the fruit itself gains largely in size and quality. In 

 our poultry, a large tuft of feathers on the head is gener- 



