DISTINCTION BETWEEN PLANTS AND ANIMALS. 347 



spontaneous movements which we are unable to distinguish in 

 character from those of the lowest animals (16), at least from those 

 made by cilia. 



663. When we consider that the excitability of sensitive plants 

 is often transmitted, as if by a sort of sympathy, from one part to 

 another ; that it is soon exhausted by repeated excitation (as is 

 certainly the case in Dionsea, the Sensitive Plant, &c.), and is only 

 renewed after a period of repose ; that all plants require a season 

 of repose ; that they evolve heat under special circumstances (372 

 -374) ; that, as if by a kind of instinct, the various organs of the 

 vegetable assume the positions or the directions most favorable to 

 the proper exercise of their functions and the supply of their wants, 

 to this end surmounting intervening obstacles ; when we consid- 

 er in this connection the still more striking cases of spontaneous 

 motion that the lower Algse exhibit, and that all these motions are 

 arrested by narcotics, or other poisons, the narcotic and acrid 

 poisons even producing effects upon vegetables respectively analo- 

 gous to their different effects upon the animal economy; we can 

 hardly avoid attributing to plants a sensibility and a power of 

 " making movements tending to a determinate end," not different 

 in nature, so far as we know, from those of the lowest animals. 

 Probably the vitality is essentially the same in the two kingdoms ; 

 and to this, faculties and attributes are superadded in the lower 

 animals, some of which are here and there not indistinctly fore- 

 shadowed in plants. 



664. Finally, if called upon to define a plant, or draw the line 

 between the animal and the vegetable kingdoms,, we can only say, 

 1. That plants alone, under the solar influence, create organic 

 matter from inorganic materials, and alone live, or are capable of 

 living, by direct aggression upon the mineral world. Consequent- 

 ly, they alone decompose carbonic acid, and render free oxygen 

 gas to the atmosphere (Chap. VI.) : the action of animals upon the 

 air is uniformly and continually the reverse. 2. In its structure, 

 a plant may be reduced to a single simple vesicle of cellular tissue 

 (94), containing chlorophyll, or its equivalent. But a developed 

 animal of the very lowest grade has a more complex structure : 

 from the necessity of the case it possesses a mouth and a stomach. 

 Indeed, we have reason to believe that the polygastric animalcules 

 are considerably complicated in structure. 3. As to chemical 

 composition, the tissue of plants, or the material of which the fab- 



