OUTLINES OF BOTANY. xli 



182. Natural Orders themselves (of which we reckon near 200) are often 

 in the same manner collected into Classes 5 and where Orders contain a 

 large number of genera, or genera a large number of species, they require 

 further classification. The genera of an Order are then collected into minor 

 groups called Tribes, the species of a genus into Sections, and in a few 

 cases this intermediate classification is carried still further. The Dames of 

 these several groups the most generally adopted are as follows, begin nmg 

 with the most comprehensive or highest :— 



Classes. Genera. 



Subclasses or Alliances. Subgenera. 



Natural Orders or Families. Sections. 



Suborders. Subsections. 



Tribes. Species. 



Subtribes. Varieties. 

 Divisions. 

 Subdivisions. 



183. The characters (3) by which a species is distinguished from all 

 other species of the same genus are collectively called the specific character 

 of the plant ; those by which its genus is distinguished from other genera 

 of the Order, or its Order from other Orders, are respectively called the 

 generic or ordinal characters, as the case may be. The habit of a plant, of 

 a species, a genus, etc., consists of such general characters as strike the eye 

 at first sight, such as size, colour, ramification, arrangement of the leaves, 

 inflorescence, etc., and are chiefly derived from the organs of vegetation. 



184. Classes, Orders, Genera, and their several subdivisions, are called 

 natural when, in forming them, all resemblances and differences are taken 

 into account, valuing them according to their evident or presumed impor- 

 tance ; artificial, when resemblances and differences in some one or very 

 few particulars only are taken into account independently of all others. 



185. The number of species included in a genus, or the number of 

 genera in an Order, is very variable. Sometimes two or three or even a 

 single species may be so different from all others as to constitute the entire 

 genus ; in others, several hundred species may resemble each other so much 

 as to be all included in one genus ; and there is the same discrepancy in 

 the number of genera to a Family. There is, moreover, unfortunately, in 

 a number of instances, great difference of opinion as to whether certain 

 plants differing from each other in certain particulars are varieties of one 

 species or belong to distinct species ; and again, whether two or more 

 groups of species should constitute as many sections of one genus, or dis- 

 tinct genera, or tribes of one Order, or even distinct Natural Orders. In the 

 former case, if a species is supposed to have a real existence in nature, the 

 question may be susceptible of argument, and sometimes of absolute proof. 

 But the place a group should occupy in the scale of degree is very arbitrary, 

 being often a mere question of convenience. The more subdivisions upon 

 correct principles are multiplied, the more they facilitate the study of 

 plants, provided always the main resting-points for constant use, the Order 

 and the Genus, are comprehensive and distinct. But if every group into 

 which a genus can be divided be erected into a distinct genus, with a sub- 

 stantive name to be remembered whenever a species is spoken of, all the 

 advantages derived from the beautiful simplicity of the Linnaean nomen- 

 clature are gone. 



