xxxii INTRODUCTION. 



While, however, the impracticability of absolute definitions is thus 

 insisted upon, there can be no doubt that much more precision may be 

 introduced than is too frequently found among them. Exceptions, although 

 to some extent inevitable, are not uncommonly apparent, not real. It will 

 frequently be found that a particular species is at variance with the defini- 

 tion of its Genus, or of a Genus with that of its Order, or of an Order with 

 that of its Alliance ; but, upon a full examination of all the structure of such 

 supposed exceptions, it will turn out that they are misplaced, and do not in 

 fact belong to the station which they occupy. Exceptions of this kind were 

 formerly very common, but they are disappearing under the diligent cri- 

 ticism of modern observers. The genus Rhynchotheca may be taken as an 

 example. The great feature of the Cranesbills is their beaked torus and 

 folded-up embryo, and it is by that circumstance that they are essentially 

 distinguished from their neighbours. But Rhynchotheca was described as 

 having a beaked fruit and straight embryo ; it therefore formed an apparent 

 exception to the definition of Cranesbills. Investigation of the plant has 

 however shown that its beak belongs to the carpels and not to the torus ; and, 

 therefore, it is merely an Oxahd, with a tendency towards the structure 

 of a Cranesbill. 



The manner in which the foregoing principles have been applied to prac- 

 tice has difi'ered greatly, and the result has been schemes of various degrees 

 of merit, some of which have dropped still-born from the press, while others 

 continue to enjoy a weU-deserved reputation. It would be aUke unjust to 

 their authors and the public to omit all mention of even the most obscure 

 of these, each of which has been the result of much thought and patient 

 study, and has doubtless contributed something to the progress of system- 

 atic science. But it would be beyond the object of the present sketch to 

 treat them all at length, nor would the student derive any advantage from 

 doing so. While, therefore, the following pages wiU be occupied by some 

 account of every plan for a Natural classification of which I have any know- 

 ledge,* since the year 1789 inclusive, and of those of Ray and Linnaeus of 

 an earlier date, such as are comparatively unimportant will be dismissed in 

 a few words, and those only which have been really employed in practice 

 will be stated at length. In order to render the latter more useful, references 

 are given to the pages in the present work where an account of each Order 

 may be found ; so that those who are accustomed to the use of other sys- 

 tems may not experience inconvenience from the arrangement proposed in 

 the work now submitted to their consideration. 



* I do not, however, include the arrangements of the German Naturphilosophists ; not, indeed, 

 from any disrespect to those learned men, but because I must confess my inability to master their ideas, 

 or to comprehend how their views are made applicable to any intelligible classification. The student ^vill, 

 I believe, find full information upon the subject in Oken's Lehrhuch der Naturpkilosophie, edition of 

 1843. See also Reichenbach's Conspectus Regni Vegctahilis, 1828, the same author's Flora Oerma- 

 nica Excursoria, 1830-2, and Schultz Naturliches Si/stern des PJlanzenreichs, 1832, 



