XXXIV INTRODUCTION. 



connected with the subject are neither slight nor easily to be 

 overcome. If these observations are properly attended to, no one 

 can be at a loss to understand, that to define any group of plants, 

 of what rank soever, is impracticable ; that differences of structure 

 are of an uncertain and unequal value; and that the affinities of 

 plants are never to be absolutely made out by solitary characters, 

 but depend upon more or less intricate combinations, the power 

 of judging of which is the same test of a skilful botanist, as an 

 appreciation of symptoms is that of a physician. 



