186 SYSTEMATIC BOTANY. 



families. It seizes upon every character wherein plants 

 agree or disagree, and forms its associations only upon 

 the principle of natural affinity. Hence, each member 

 of any natural group resembles the other members ; 

 and a fair description of one will serve, to a certain 

 extent, for all the rest. 



464. The species and genera are formed on this 

 principle of classification, as above stated, and are 

 truly natural associations. Individuals altogether simi- 

 lar cast, as it were, in the same mold constitute a 

 species. Species agreeing in nearly all respects, and 

 differing but in few, constitute a genus. Thence the 

 genera, associated by their remaining affinities in 

 groups of few or many, by this same method are 

 organized into Natural Orders and other departments 

 of the System. 



CHAPTER II. 



NATURAL SYSTEM. 



465. Botanists during the last two hundred years 

 have labored to group and arrange the individuals of 

 the vegetable kingdom so that the natural characters 

 of each group shall be most like those of the next 

 preceding group. 



466. In 1694, Tournefort, a French physician and 

 botanist, published a method of arrangement in which 

 he defined and established the term genus as we now 

 understand it. 



467. Early in 1700, John Ray, an English natu- 

 ralist, separated the vegetable kingdom into the fol- 

 lowing general groups ; 



