PLANTS. - The leaf of the higher plants, is the unit or individual of botanists, is bilateral and symmetrical—always in idea, generally in fact. These leaves are associated together to form buds, branches, flowers, or fruits, in whorls. Symmetrical figures are often produced by these associations, but yet the pattern is spiral. In watching the develop ment of spores of conferva, they are seen, whilst still but single cells, to shoot out in various manners, the majority of which are quite irre concilable with symmetry, either bilateral or ra diating. Whatever may be its import,: it is quite certain, from the very nature of symmetry, that the cause of it must be internal, that is to say, within the holy in which it is inani fested. But it has been conclusively deter mined, by experiments, that external influences, acting upon them in certain directions only, such as light, heat, and gravitation, exert a considerable power in determining the form of vegetable productions. Animals, doubt
less, are also greatly affected by these agencies, yet, as they enjoy the faculty of locomotion whereby all parts of them are successively turned towards the directions from which these forces emanate, the form impressed upon them by internal causes, suffers little or no distortion therefrom; but plants, being destitute of locomotion, continually receive these influences in a partial manner, and con sequently we the less expect to meet with symmetry among them. Whenever their in ternal forces tend to make them symmetrical, the partial action of external agents is apt to disturb their symmetry. It is this, probably, that renders the germinating conferva cell unsymmetrical.