18 II, OEDEES AND GENEEA. 



may be conceded by those who are least of slaves to the 

 trammels of system-making, that botanical arrangements 

 in books do bear an accordance with the realities of na- 

 ture. Yet that accordance is imperfect and partial. In 

 many received groups some widely dissimilar plants are 

 brought together by very partial resemblances ; and, in 

 other instances, certain closely similar plants are thrown 

 into diiferent groups by single or partial differences. So 

 to express this circumstance, — if we look inside tlie 

 boundaries of one order, we there find heterogeneous 

 constituents ; — if we look at the conterminous boundaries 

 of allied orders, we find them separating homogeneous 

 ingredients. 



The same is true in respect of genera. The example 

 of Eleocharis, above cited, is an instance of a natural 

 group split by an arbitrary character, so as to throw ho- 

 mogeneous sj)ecies into different genera ; for Eleocharis 

 multicaulis much more closely resembles Scirpus pauci- 

 florus, than this latter resembles Scirpus sylvaticus ; and 

 so with other species. But as genera are minor and sub- 

 ordinate groups, which can be divided and subdivided to 

 almost any extent, short of splitting species in so doing, 

 the examples of heterogeneous species brought under the 

 same generic name, are not so decided as those of hete- 

 rogeneous genera placed in the same order. Indeed, 

 this kind of evidence, as to the optional or arbitrary cha- 

 racter of generic groups, might almost disappear under 

 the modern practice of increasing generic divisions at 

 will, — reconverting the groups into gradations, — were it 

 not kept up to some extent by a peculiarity of generic 

 groups, which does not equally belong to orders and 

 species. 



It is customary with writers on elementary botany, to 

 represent genera as groups intermediate between orders 



