SECTION 18.] CLASSIFICATION. 175 



Section XVIII. CLASSIFICATION AND NOMENCLATURE. 



519. Classification, in botany, is the consideration of plants in respect 

 to their kinds and relationships. Some system of Nomenclature, or nam- 

 ing, is necessary for fixing and expressing botanical knowledge so as to 

 make it available. The vast multiplicity of plants and the various degrees 

 of their relationship imperatively require order and system, not only as to 

 names for designating the kinds of. plants, but also as to terms for defining 

 their differences. Nomenclature is concerned with the names of plants. 

 Terminology supplies names of organs or parts, and terms to designate 

 their differences. 



§ 1. KINDS AND RELATIONSHIP. 



520. Plants and animals have two great peculiarities : 1st, they form 

 themselves ; and 2d, they multiply themselves. They reproduce their kind 

 in a continued succession of 



521. Individuals. Mineral things occur as masses, which are divisible 

 into smaller and still smaller ones without alteration of properties. But 

 organic things (vegetables and animals) exist as individual beings. Each 

 owes its existence to a parent, and produces similar individuals in its turn. 

 So each individual is a link of a chain ; and to this chain the natural- 

 historian applies the name of 



522. Species. All the descendants from the same stock therefore com- 

 pose one- species. And it was from our observing that the several sorts of 

 plants or animals steadily reproduce themselves, or, in other words, keep 

 up a succession of similar individuals, that the idea of species originated. 

 There are few species, however, in which man has actually observed the 

 succession for many generations. It could seldom be proved that all the 

 White Pine trees or White Oaks of any forest came from the same stock. 

 But observation having familiarized us with the general fact that indi- 

 viduals proceeding from the same stock are essentially alike, we infer from 

 their close resemblance that these similar individuals belong to the same 

 species. That is, we infer it when the individuals are as much like each 

 other as those are which we know, or confidently suppose, to have sprung 

 from the same stock. 



523. Identity in species is inferred from close similarity in all essential 

 respects, or whenever the differences, however considerable, are not known 

 or reasonably supposed to have been originated in the course of time under 

 changed conditions. No two individuals are exactly alike ; a tendency to 

 variation pervades all living things. In cultivation, where variations are 

 looked after and cared for, very striking differences come to light ; and if 

 in wild nature they are less common or less conspicuous, it is partly be- 

 cause they are uncared for. When such variant forms are pretty well 

 marked they are called 



