OUTLINES OF BOTANY. xli 
182. Natural Orders themselves (of which we reckon near 200) are often 
in the same manner collected into Classes; 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 names of 
these several groups the most generally adopted are as follows, beginning 
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 toa 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 Linnean nomen- 
clature are gone. | 
