LAWS OF VARIATION 119 



elder De Candolle founded his main divisions in the order on such 

 characters. Hence modifications of structure, viewed by system- 

 atists 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 struc- 

 tures 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 in- 

 dependent 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 cor- 

 related. 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 im- 

 possibility of seeds gradually becoming winged through natural 

 selection, unless the capsules were open: lor 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 

 excess, to another part; thus it is difficult to get a cow to give 

 much milk and to fatten readily. The same varieties of the cab- 

 bage do not yield abundant and nutritious foliage and a copious 

 supply of oil-bearing seeds. When the seeds in our fruits become 

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

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

 companied by a diminished comb, and a large beard by diminished 

 wattles. With species in a state of nature it can hardly be main- 

 tained that the law is of universal application; but many good 

 observers, more especially botanists, believe in its truth. I will 

 not, however, here give any instances, for I see hardly any way 

 of distinguishing between the effects, on the one hand, of a part 

 being largely developed through natural selection and another and 



