20 THE ELEMENTARY STRUCTURE OF PLANTS. 



permanent internal repose : whatever changes it undergoes are 

 owing to the action of some extraneous force, not to any inherent 

 power. This holds true even in respect to the chemical combina- 

 tions which occur in the mineral and in the organic kingdoms. In 

 the former they are stable ; in the latter they are less so in pro- 

 portion as they are the more under the influence of the vital prin- 

 ciple: as if in the state of unstable equilibrium, a comparatively 

 slight force induces retrograde changes, through which they tend 

 to reassume the permanent mineral state. 6. Consequently the 

 duration of living beings is limited. They are developed, they 

 reach maturity, they support themselves for a time, and then perish 

 by death, sooner or later. Mineral bodies have no life to lose, and 

 contain no internal principle of destruction. Once formed, they 

 exist until destroyed by some external power ; they lie passive 

 under the control of physical forces. As they were formed irrespec- 

 tive of the pre-existence of a similar body, and have no self-deter- 

 mining power while they exist, so they have no power to determine 

 the production of like bodies in turn. The organized being may 

 perish, indeed, from inherent causes ; but not until it has given rise 

 to new individuals like itself, to take its place. The faculty of re- 

 production is, therefore, an essential characteristic of organized 

 beings. 



13. Individuals. The mass of a mineral body has no necessary 

 limits ; a piece of marble, or even a crystal of calcareous spar, 

 may be mechanically divided into an indefinite number of parts, 

 each one of which exhibits all the properties of the mass. But 

 plants and animals exist as individuals; that is, as beings, com- 

 posed of parts which together constitute an independent whole, that 

 can be divided only by mutilation. Each owes its existence to a 

 parent, and produces similar individuals in its turn. So each in- 

 dividual is a link of a chain ; and to this chain the natural-historian 

 applies the name of 



14. Species. The idea of species is therefore based upon this suc- 

 cession of individuals, each deriving its existence, with all its peculi- 

 arities, from a similar antecedent one, and transmitting its form 

 and other peculiarities essentially unchanged from generation to 

 generation. By species we mean abstractly the type or original 

 of each sort of plant, or animal, thus represented by a perennial 

 succession of like individuals : or, concretely, the species is the sum 

 of such individuals. 



