362 



CLASSIFICATION. 



points of agreement or difference, are employed in their classifica- 

 tion ; those which are common to the greatest number of plants 

 being used for the primary grand divisions ; those less compre- 

 hensive for subordinate groups, &c. ; so that the character (678), 

 or description of each group, when fully given, actually expresses 

 all the known particulars in which the plants it embraces agree 

 among themselves, and differ from other groups of the same rank. 

 This complete analysis being carried through the system, from the 

 primary divisions down to the species, it is evident that the study 

 of a single plant of each group will give a correct general idea of 

 the structure, habits, and even the sensible properties, of the whole. 



686. What we call a natural method, it may here be remarked, 

 is so termed merely because it expresses the natural relationship 

 of plants as far as practicable ; for every form yet contrived, or 

 likely to be devised, is, to a considerable extent, artificial : 

 1st. Because the affinities of a particular group cannot be fully 

 estimated until all its members are known ; and thus the progress 

 of discovery leads to changes, or modifies our views, as in every 

 other department of knowledge. 2d. Because the boundaries of 

 groups are not so arbitrarily circumscribed in nature, as they ne- 

 cessarily are in our classifications ; but individuals depart from the 

 assigned limits in various directions (like rays from a centre) ; 

 the " edge of difference being, as it were, softened down by an 

 easy transition." 3d. Because, even supposing the groups to be 

 perfectly natural, and their affinities completely understood, it is 

 impossible to arrange them in a single continuous series, in such a 

 manner that each shall be preceded and followed by its nearest 

 allies ; since the same family, for instance, may be about equally 

 related to three or four others, only two of which points, at best, 

 can be indicated in the lineal series which must be adopted in 

 books. And 4th. We are still obliged to use avowedly artificial 

 characters, for the sake of convenience ; as in the arrangement of 

 the numerous orders of Exogenous plants into the Polypetalous, 

 Monopetalous, and Apetalous divisions of the series, although dif- 

 ferent genera of the same order, or different species of the same 

 genus, may present these very diversities. 



687. In explaining the general principles of classification, we 

 proceeded from the individual to the class ; showing how groups 

 of successive rank arise from the consideration of points of agree- 

 ment. In applying them to the actual distribution of plants ac- 



