in Natural History. 489 
Division and separation is the end of the artificial system ;— 
to establish agreements is the end of the natural. In one case 
we reason à priori; in the other à posteriori. The one is a 
descending, the other an ascending series. Linnæus under- 
stood this distinction when he remarked, ** Ordines naturales 
valent de naturá plantarum ; artificiales in diagnosi plantarum." 
—** Cavendo in imitando naturam filum Ariadneum amittamus.” 
Nevertheless it has appeared to me that many modern natu- 
ralists have not adopted these truths ; and that it is the prevalent 
error of the day to attempt to generalize where they ought to 
analyse; while their arrangements, called natural, are almost 
all of them framed with a view to distinguish. Let me not be 
supposed by these remarks to wish to exclude from the natural 
system every attempt at diagnosis; for it is obvious, that as the 
business of the naturalist is to study all the characters, he can 
no more neglect differences than he can agreements. I only 
wish to point out the two dissimilar objects we have in view, 
| that they may not be confounded. 
M. Decandolle, for instance, whose labours asa systematist 
are invaluable, seems to overlook this distinction. In his ** Regni 
Vegetabilis Systema Naturale," he starts from things the least 
known, to reason on things best known. He begins his compre- 
hensive work with a predicate of the stars; and, proceeding 
downwards to minerals, comes to plants. Here he employs a 
series of terms expressive of a natural gradation from the highest 
to the lowest group, attempting fresh combinations at every stage, 
and making a place for every thing. Thus he has class, sub-class, 
cohort, order, tribe, genus, section, species. The extraordinary 
number of these combinations diminishes their value as a work of 
natural arrangement. It is a difficulty of sufficient amount to 
establish a few well marked ; and when they are so multiplied, it 
may be suspected that many of them are arbitrary and artificial. 
8 r 2 This 
