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variations, until those marked differences are produced which 

 distinguish the actually existing species in nature. Valuable 

 results, however, in the way of producing new forms have been 

 obtained in horticulture and agriculture by a combination of 

 the operations of selecting the best strains, of crossing distinct 

 strains, and of selecting for propagation those individuals which 

 exhibit the most desirable fluctuating variations, and we must, 

 therefore, be careful not to hastily ascribe to any one type of 

 variation, or to any single factor, pre-eminent importance in the 

 evolution of species in nature. 



