INTRODUCTION. 



xlix 



From this it appears, that out of 173 genera belonging to fourteen 

 Linnean sections, no fewer than forty -three genera, or nearly one quarter, 

 contain species at variance with the characters of the classes and orders in 

 which they are placed. Were general works on Botany examined in the 

 same manner, it would be found that the proportion of exceptions is at 

 least as great as that indicated by the foregoing table, which comprehends 

 only those species, the variations of which are constant and uniform, and 

 does not include mere accidental deviations, such as the tendency of 

 Tetrandrous flowers to become Pentandrous, of Pentandrous to become 

 Tetrandrous, or of both to become Polygamous. 



Although this is not stated for the purpose of extolling the Natural 

 System at the expense of the Linnsean, but rather, as has just been re- 

 marked, for the sake of doing away with a vulgar prejudice, yet I cannot 

 forbear expressing my doubt whether any fourteen natural orders can be 

 named in which the proportion of exceptions is so considerable as this, 

 namely, more than one in five. 



Upon the supposed peculiar difficulties of the Natural System I have 

 elsewhere made some general remarks (Synopsis, p. x.), which need not 

 be repeated here. It will be better now to inquire more particularly in 

 what the difficulty consists. 



It is said that the primary characters of the classes are not to be ascer- 

 tained without much laborious research ; and that not one step can be 



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