THE PRINCIPLES OF CLASSIFICATION. 325 



644. The genus must be based on close relationship of species, 

 but not necessarily on the closest. Raspberries differ from 

 Blackberries, but must be ranked in the same genus ; and so of 

 Plums and Cherries. For the groups which are to bear the 

 generic name must be as distinct and definite as possible. 



645. Orders are to genera what genera are to species. They 

 are groups of a higher rank and wider comprehension, expressive 

 of more general resemblances, or, in other language, of remoter 

 relationship. As all species must be ranked in genera, so all 

 genera must be ranked in orders. FAMILY in botany is synony- 

 mous with order : at least natural orders and families (however 

 distinguished in zoology) have always in botany been inter- 

 changeable terms, and will probably so continue. 1 



646. As examples of orders in the vegetable kingdom take 

 the Oak family, composed of Oaks, Chestnuts, Beeches, &c. ; 

 the Pine family, of Pines, Spruces, Larches, Cedars, Araucaria, 

 Cypresses, and their allies ; the Rose family, in which Brambles, 

 Strawberries, Plums and Cherries, Apples and Pears are asso- 

 ciated with the Rose in one somewhat multifarious order. 



647. Classes are to orders what these are to genera. They 

 express still more comprehensive relations of species ; each class 

 embracing all those species which are framed upon the same 

 broad plan of structure, however differently that plan may be 

 carried out in particulars. 



648. Kingdom must be added, to represent the highest gener- 

 alization. All subjects of biological classification belong either 

 to the vegetable or animal kingdom. Mineralogy, Chemistry, 

 &c., ma}' use the same terms (genus, species, &c.) in an analo- 

 gous way ; but the classification of substances rests on other 

 foundations than that of beings. 



649. The sequence of groups, rising from particular to univer- 

 sal, is Species, Genus, Order, Class, Kingdom ; or, in descending 

 from the universal to the particular, 



KINGDOM, 

 CLASS, 



ORDER, 



GENUS, 



SPECIES. 



1 Order is the older term, and that which associates best with the technical 

 Latin names. Family is a happy term, which associates itself well with 

 English names. But its use is attended with this incongruity, that the tribe 

 (653) in natural history classification is subordinate to the family. In 

 zoology, order is distinguished from family as the next higher grade. 



