VITAL CHARACTERISTICS OF PLANTS. 395 



tion." The microscopist sees proof of a higher life in plants than he 

 before conceived ; and he becomes convinced, after examining the 

 functions which their organs are destined to perform, that animals and 

 plants are only separate links in the great chain of organic nature. 



Plants are organised beings ; that is, individuals composed of a 

 number of essential and mutually dependent parts : in common, there- 

 fore, with animals, they possess a principle which is in continued 

 action; and which operates in such a manner, that the individual parts 

 which it forms in the body are adapted to the designs of the whole. 

 Or, in more intelligible language, plants are living bodies. Like ani- 

 mals, they are the offspring of other beings similar to themselves; they 

 grow, are endowed with excitability, have their periods of infancy, adult 

 age, decay, and death. Their affinity to animals is much closer than is 

 commonly supposed. The vital or creative power exists already in the 

 germ, in plants as well as in animals ; and by its influence the essential 

 parts of the future plant are formed. It might be supposed that the 

 lateral generation of plants namely, that renewal of the individual 

 which is the result of budding or gemmation is sufficient to distin- 

 guish them from animals ; but this opinion is erroneous, as we find 

 that the formation of gems or buds is common in animals belonging to 

 the Protozoa. In the hydra, we perceive the germs developed as small 

 ovoid elevations upon the cylindrical body of the animal, and when 

 examined in this state, they are, like the first formation of the buds in 

 plants, mere masses of cells ; but as their growth proceeds, these cells 

 undergo a special arrangement, so as to produce the different tissues 

 of the body, and acquire the proper form of the polyp : on the same 

 principle, the bud in the plant is gradually developed, until it termi- 

 nates, and becomes a branch. 



Plants, like animals, possess excitability, or the faculty of being 

 acted upon by external stimuli, impelling them to the exertion of their 

 vegetable powers. Light acts on plants, directing the growth of the 

 stem, vigour, and colour, the direction of the branches, position of 

 leaves, the opening and shutting of flowers. Heat influences the pro- 

 trusion of buds, and other stimulants affect the vegetable irritability ; 

 as an instance of this, cut plants, when fading, revive if placed in water 

 impregnated with certain chemicals. 



Besides the physical and physiological distinctions generally pointed 

 out as marking the line between animals and plants, chemistry furnishes 

 many others. Thus, one of the great functions of a plant is to decom- 

 pose water, and assimilate its components to the vegetable tissues ; 

 whilst it is a property of animal life constantly to reform it from its 



