3G0 PRINCIPLES OF CLASSIFICATION. 



They are groups of kindred genera, or rather genera of a Incjher 

 grade. For example, Oaks, Chestnuts, Beeches, Hazels, and Horn- 

 beams constitute so many genera, which, although quite distinct, have 

 so strong a family likeness, and are so much alike in their general 

 structure and properties, that they are associated into one order or 

 family group (the Oak family) ; while the Birches and the Alders 

 form another order not very different in character, and the Walnuts 

 and Hickories another. So the Pines, Firs or Spruces, Larches, 

 Cedars, &c., obviously related among themselves so much more than 

 they are to any other genera, are members of the Pine family ; the 

 Raspberry, Blackberry, and Sti'awberry, with many others, ai'e as- 

 sociated with the Rose in the Rose family ; and so on. 



701. Classes are to orders what these are to genera. They ex- 

 press more extensive, or the most extensive relations of species, each 

 class embracing all those species which are framed upon the same 

 general plan of structure, however differently that plan may be 

 carried out in particulars. Thus all Exogenous or Dicotyledonous 

 plants constitute one class, their stems, their embryo, their leaves, 

 &c. being constructed upon the same general plan in all the species, 

 while Endogenous or Moncotyledonous jjlants for the same reasons 

 compose another class. 



702. The sequence of groups, rising from particular to universal, 

 is Species, Genus, Order, Class ; or, in descending from the univer- 

 sal to the particular. 



Class, 



Order, 



Genus, 



Species. 



703. These are the common framework of all methods of classifi- 

 cation, both in the animal and the vegetable kingdoms. But these 

 do not exhaust our powers of analysis, nor express all the gradations 

 which we may observe in the relationship of species. They merely 

 gather up wliat are deemed the most essential indications of re- 

 lationship, and express them under three grades superior to species, 

 which always carry with them distinctive names. But a more elab- 

 orate analysis is often requisite, on account of the large number 

 of objects to be arranged, and the various degrees of relationship 

 which may come into view. And these, Avlien needful, are expressed 

 in a series of intermediate groups or divisions, which may or may 

 not require distinctive niuues. Names for them are, llowe^^er, a 



