rNTEODUCTio?r. 27;' 



family, 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 

 other cases several hundred species may resemble each other so much as to 

 be aU included in one genus, and there is the same discrepancy in the num- 

 ber of genera to each family. 



Those particulars in which aU the individuals of a species resemble each 

 other, and by which they diifer from all other species, are called characters 

 of tlie species ; they altogether form the specific character of a plant. So 

 also those particulars in which all the species of a genus resemble each otner, 

 and by which they differ from aU other genera, are characters of the genus,- 

 and collectively the generic character of the plant. 



Families themselves are often in the same manner collected into Classes, 

 and where families contain a large number of Genera, or Genera a large 

 number of species, they require further classification. The genera of a 

 femily are collected into minor groups, called Tribes, the species of a genus into 

 Sections, and in a few cases, tliis intermediate classification is carried stiU 

 further. The names of these several groups, the most generally adopted,- 

 are as follows, beginning with the largest, commonly called the highest : — 



Classes. Genera. 



Subclasses or Alliances. Subgenera. 

 Families or Natxiral Orders. Sections. 



Suborders. Subseclions. 



Tribes. Species. 



Sultribes. Varieties. 

 Divisions. 

 Subdivisions. 



Classes, FamLhes, Geneva, and their several subdivisions, are called 

 natural, when, in forming them, aU 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. 



There is unfortunately, in a number of instances, great difference of opinion 

 as to whether certam plants differing from each other in certain particulars, 

 are varieties of one species, or belong to distinct species ; and again, whe- 

 ther two or more groups of species should constitute as many sections of one 

 genus, or distinct genera, or tribes of one family, or even distinct famUies. 

 In the former case, as a species is supposed to have a real existence in 

 nature, the question is susceptible of argument, and sometimes of absolute 

 proof. But the place a group should occupy in the scale of degree is very 

 arbitrary, being a mere question of convenience. The more subdivisions 

 upon correct principles are midtiplied, the more they facihtate the study of 

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

 and the genus, are comprehensive and distinct. But if every gi-oup into 

 which a genus can be divided is 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 simphcity of the Linnean nomencla- 

 ture are gone. 



