No. Xni.] APPENDIX. 



215 



body whicli exists by means of forces exerted between tbe particles of 

 matter of whicli the mass is made up. 



Proceeding onwards in onr investigation, we perceive another class of 

 bodies said to be organic, the particles of which are continually under- 

 going some change of arrangement. The most simple division of this 

 class of bodies is to be found in vegetables or plants, samples of which I 

 now present to your notice in the India-rubber tree, the black-tea plant, 

 and the beautiful filmy fern. We find that the material has tenacity and 

 form, from a certain amount of the particles of which they are composed 

 being held together by internal forces similar to those of inorganic bodies. 

 In this respect stones and plants are identical ; both having matter and 

 internal forces. In the latter, however, we have continual changes occurring, 

 and the mechanism of this change gives to the vegetable its characteristic 

 property. In every plant we find that it is essential to vitality that it 

 should contain not only a solid portion, but also a fluid : hence a plant is 

 in two physical states, solid and fluid ; in other words, it consists of stem 

 and sap. Neither part alone exhibits any signs of life ; a combination of 

 both being required for that object. But the stem and sap, as a whole, 

 wiU not exhibit change by means of forces generated alone within its own 

 structure, for we find it to be essential for these results that external 

 forces should act upon the whole plant to enable these alterations in the 

 aiTangement of its particles to ensue. The absolute necessity for the 

 exertion of these external forces may be learnt from the fact, that if I 

 either increase or diminish the amount requisite for each plant, the 

 actions immediately cease ; and if they cease but for one instant, the matter 

 becomes inorganic, and no human power can ever make it take on the 

 changes occurring in the vegetable or plant. If either this India-rubber 

 tree or tea-plant were frozen, its action would cease for ever; and in 

 the same way, if this delicate filmy fern, or even the other plants, were 

 either to be over-heated or stimulated too highly by light, electricity or 

 force, they would certainly perish. We thus find that a plant is a body 

 held together by internal forces in two physical states, solid and fluid, 

 undergoing certain changes by means of the action of external forces. As 

 a consequence of this arrangement, a plant cannot be indefinitely divided ; 

 for to possess the characteristics of a plant it must retain aU these essen- 

 tials, and we cannot divide it if we desire to preserve its individuality 

 beyond a single cell. As a short expression for the difference between 

 plants and stones, we may state that a plant is a body whose particles are 

 undergoing change from the action of forces from without. This pro- 

 perty, I shall hereafter show you, is common to all organic bodies, so that 

 definition can only be used to ascertain whether a body is a mineral or a 

 vegetable. This expression harmonizes with the phenomena observed in 

 aU the numerous forms of plants habitating the globe ; one plant differing 

 from another not by its possessing some new attribute, but from a differ- 

 ence in the nature of the matter which composes its structure, the degree 

 of force holding that matter together, the ease with which its particles 

 assume new combinations, and the amount of external force required to 

 effect that change. Every species of plant of necessity requires a peculiar 

 amount of external force. If the filmy fern which inhabits the cracks and 

 crannies of the rocks at Tunbridge Wells were exposed to the light 

 which this tea-plant requires, it would speedily be killed, and this tea- 



