SECT. II. TAXONOMY AND PHYTOGRAPHY. 137 



in the first place, the limits within which a given 

 species might be supposed to vary. Then, by com- 

 paring different species, and selecting those which had 

 the greatest resemblance, a genus was constructed. 

 Then the genera were grouped into orders ; and lastly, 

 those orders which possessed only a few general but im- 

 portant points of resemblance, were arranged under the 

 three classes alluded to. But when these several groups 

 were once established, a further refinement in their 

 classification could be made ; and the principles upon 

 which this was effected, may be explained by the ana- 

 lytical process to which we have just had recourse, 

 when we said that all species are comprised, first, in a 

 class; secondly, in an order, or family ; and thirdly, 

 in a genus. In very many cases, a further subordination 

 may be established among the several groups ; and, 

 from various considerations, they may either be aggre- 

 gated into larger, or subdivided into smaller groups ; to 

 which other names are applied, of which we have 

 given an example in art. 102. . When any group is 

 subdivided into larger groups than those which it 

 is supposed to contain under the system of subordin- 

 ation already described, these are generally recognised 

 by the addition of the word " sub" to the name of 

 the original group ; thus we have sub-classes, sub- 

 orders, and sub-genera. Certain groups are also termed 

 " Tribes," " Cohorts," " Sections," and Divisions ; " 

 and some of these terms are used indiscriminately for 

 subordinate groups among the classes, genera, and even 

 species. When a " variety" of any species is repro- 

 ducible by seed, and retains its peculiarities pretty 

 steadily, without returning to the more common type, 

 it is termed a "race;" but when its distinguishing 

 characters are transient, and may be modified by a 

 change of soil or situation, it is only a "variation." 

 In this way then, we establish a subordination among 

 the natural groups into which plants may be arranged, 

 and which may be exemplified by the following in- 

 stance. 



