THE NATURAL SYSTEM. 87 



plants they comprehend, to assume a particular mode of deve- 

 lopement. 



642. Their characters are therefore nothing more than a 

 declaration of their prevailing tendencies, and are liable to 

 numerous exceptions. 



This liability, it must be remarked, exists as much in all artificial schemes as in 

 the natural system itself. 



643. If a system is ever to be devised which shall by com- 

 mon consent be admitted to be natural in all its parts, as 'far 

 as human means can make it so, this will be brought about 

 by settling the relative value of the characters by which 

 plants are limited, and by introducing uniformity and con- 

 sistency into the distinctions of the groups, whether inferior, 

 superior, or intermediate. 



Up to the present time, no attempt at settling these points has been successful, 

 and consequently the characters employed in denning the limits of groups, 

 of all denominations except the highest, are arbitrary and inconsistent. 



644. The following propositions seem incontrovertible : 



1. Nothing that is constant can be regarded as unimportant. 



2. Every thing constant must be dependent upon or con- 

 nected with some essential function. Therefore all constant 

 characters, of whatever nature, require to be taken into 

 account in classifying plants according to their natural affi- 

 nities. 



Of this nature are the internal structure of stems and leaves, the anatomical con- 

 dition of tissue, the organization of the anther, pollen, and female apparatus, 

 and the interior of the seed. 



645. On the other hand, whatever points of structure are 

 variable in the same species, or in species nearly allied to each 

 other, or in neighbouring genera, are unessential to the vital 

 functions, and should be set aside, or be regarded as of compa- 

 rative unimportance. 



Hence the badness of the Monopetalous, Polypetalous, and Apetalous divisions 

 of Jussieu, depending upon the presence or absence, and union or disunion, of 

 petals. The genus Fuchsia, for example, has petals highly developed ; but in 

 F. excorticata they are absent, and yet the plant differs no otherwise from the 

 rest of the genus : the same is true of species of Rhammis. Again, the Rue 

 has the petals separate ; and Correa, very nearly allied to it, has them com- 

 bined. 



