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176. It has already been observed (3) that descriptions of plants should, as nearly as possible, be arranged under natural divisions, so as to facilitate the comparison of each plant with those more nearly allied to it. The descriptions of plants here alluded to are descriptions of species; the natural divisions of the Flora refer to natural groups of species.

177. A Species comprises all the individual plants which resemble each other sufficiently to make us conclude that they are all, or may have been all, descended from a common parent. These individuals may often differ from each other in many striking particulars, such as the colour of the flower, size of the leaf, etc., but these particulars are such as experience teaches us are liable to vary in the seedling raised from one individual.

178. When a large number of the individuals of a species differ from the others in any striking particular they constitute a Variety. If the variety generally comes true from seed, it is often called a Race.

179. A Variety can only be propagated with certainty by grafts, cutting, bulbs, tubers, or any other method which produces a new plant by the development of one or buds taken from the old one. A Race may with care be propagated by seed, although seedlings will always be liable, under certain circumstance, to lose those particulars which distinguish it from the rest of the species. A real Species will always come true from seed.

180. The known species of plants (now near 100,000) are far too numerous for the human mind to study without classification, or even to give distinct single names to. To facilitate these objects, an admirable system, invented by Linnæus, has been universally adopted, viz., one common substantive name is given to a number of species which resemble each other more than they do any other species; the species so collected under one name are collectively called a Genus, the common name being the generic name. Each species is then distinguished from the others of the same genus by the addition of an adjective epithet of specific name. Every species has thus a botanical name of two words. In Latin, the language usually used for the purpose, the first word is a substantive and designates the genus; the second, an adjective, indicates the species.

181. The genera thus formed being still too numerous (above 6,000) for study without further arrangement, they have been classed under the same principles, viz., genera which resemble each other than they do any other genera have been collected together into groups of a higher degree called Families or Natural Orders, to each of which a common name has been given. This name is in Latin an adjective plural, usually taken from the name of some one typical genus, generally the best known, the first discovered, or the most marked (e.g., Ranunculaceæ from Ranunculus). This is however for the purpose of study and comparison. To speak of a species, to refer to it and identify it, all that is necessary is to give the generic and specific names.

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 most generally adopted are as follows, beginning with the most comprehensive or highest :—

Classes Subtribes Sections
Subclasses or Alliances Divisions Subsections
Natural Orders or Families Subdivisions Species
Suborders Genera Varieties
Tribes Subgenera  

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 call the generic or ordinal character, 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 of presumed importance; 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 distinct genera, or tribes of one Order, or even distinct Natural Orders. In the former case. As a species is supposed to have a real existence in nature, the question is susceptible of argument, and sometime 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 Order and the Genus, are comprehensive and distinct. But if every group into the study of plants, provided always the main resting-points for constant use, the which a genus can be divided be erected into a distinct genus, with a substantive name to be remembered whenever a species is spoken of, all the advantages derived from the beautiful simplicity of the Linnæan nomenclature are gone.

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