3.")8 PRINCIPLKS OF CLASSIFICATION. 



grees. If this were not so, or if related species differed one from 

 another by a constant quantity, so that, when arranged according 

 to their resemblances, the first differed from the second about as 

 much as the second from the third, and the third from the fourth, 

 and so on throughout, — then, with all the diversity in the vege- 

 table kingdom there actually is, there could be no natural founda- 

 tion for their classification. The multitude of species would render 

 it necessary to classify them, but the classification would be wholly 

 artificial and arbitrary. The actual constitution of the vegetable 

 kingdom, however, as appears from observation, is, that some species 

 resemble each other very closely indeed, others differ as widely as 

 possible, and between these the most numerous and the most various 

 grades of resemblance or difference are presented, but always with 

 a manifest tendency to compose groups or associations of resembling 

 species, — groups the more numerous and apparently the less defi- 

 nite in proportion to the number and the nearness of the points of 

 resemblance. These various associations the naturalist endeavors to 

 express, as far as is necessary or practicable, by a series of generali- 

 zations, — of which the lower or particular are included in the 

 higher, — based on the more striking, or what he deems the most 

 important (i. e. the most definite or least exceptional) points of re- 

 semblance of several grades. Linnaeus and the naturalists of his 

 day mainly recognized three grades of association, or groups supe- 

 rior to species, viz. the genus, the order, and the class ; and these are 

 still the principal members of classification. Of these 



G98. Genera (plural of Genus) ai-e the more particular or special 

 groups of related species. They are groups of species which are 

 most alike in all or most l-espeets, — which are constructed, so to 

 say, upon the same particular model, with only circumstantial dif- 

 ferences in the details. They are not necessarily nor generally the 

 lowest definable groups of species, but are the lowest most clearly 

 definable groups which the botanist recognizes and accounts worthy 

 to bear the generic name ; for the name of the genus with that of 

 the species added to it is the scientific appellation of the plant or 

 animal. Constituted as the vegetable and animal kingdoms are, the 

 recognition of genera, or groups of kindred species, is as natural an 

 operation of the mind as is the conception of species from the asso- 

 ciation of like individuals. This is because many genera are so 

 strongly marked, or at least appear to be so, as far as ordinary ob- 

 servation extends. Every one knows the llo e genus, composed of 



