Chap. V.] CORRELATED VARUTION. 181 



ferences are of such apparent importance — ^the seeds 

 being sometimes orthospermous in the exterior iiowers 

 and ccElospermous in the central flowers, — ^that the 

 elder De Candolle founded his main divisions in the 

 order on such characters. Hence modifications of struc- 

 ture, 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 varia- 

 tion structures which are common to whole groups of 

 species, and which in truth are simply due to inheri- 

 tance; 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 necessary manner correlated. 

 Some other correlations are apparently due to the man- 

 ner in which natural selection can alone act. For in- 

 stance, 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 ease 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. 



