272 OPERATIONS SUBSIDIARY TO INDUCTION. 



down a theory, grounded on an important truth, which he 

 has, in some respects, expressed and illustrated very felici- 

 tously ; but also, as it appears to me, with some admixture of 

 error. It will he advantageous, for both these reasons, to 

 extract the statement of his doctrine in the very words he 

 has used. 



" Natural groups," according to this theory,* are " given 

 by Type, not by Definition." And this consideration accounts 

 for that " indefmiteness and indecision which we frequently 

 find in the descriptions of such groups, and which must 

 appear so strange and inconsistent to any one who does not 

 suppose these descriptions to assume any deeper ground of 

 connexion than an arbitrary choice of the botanist. Thus in 

 the family of the rose-tree, we are told that the ovules are 

 very rarely erect, the stigmata usually simple. Of what use, 

 it might be asked, can such loose accounts be ? To which the 

 answer is, that they are not inserted in order to distinguish 

 the species, but in order to describe the family, and the total 

 relations of the ovules and the stigmata of the family are 

 better known by this general statement. A similar observation 

 may be made with regard to the Anomalies of each group, 

 which occur so commonly, that Mr. Lindley, in his Introduction 

 to the Natural System of Botany, makes the ' Anomalies' an 

 article in each family. Thus, part of the character of the 

 Kosacese is, that they have alternate stipulate leaves, and that 

 the albumen is obliterated; but yet in Lowea, one of the 

 genera of this family, the stipule are absent; and the albumen 

 is present in another, Neillia. This implies, as we have already 

 seen, that the artificial character (or diagnosis, as Mr. Lindley 

 calls it,) is imperfect. It is, though very nearly, yet not 

 exactly, commensurate with the natural group : and hence in 

 certain cases this character is made to yield to the general 

 weight of natural affinities. 



" These views, of classes determined by characters which 

 cannot be expressed in words, of propositions which state, 

 not what happens in all cases, but only usually, of particulars 



* Hist. Sc. Id. ii. 120122. 



