“Further; The external conditions of this internal development of plants and animals, are Food, Air, and Heat; while Light seems to be a peculiar condition, indispensably necessary to plants. Where any one of these conditions is not supplied, the existence of life, whether animal or vegetable, becomes impossible; where it is insufficiently supplied, life is {256} proportionally enfeebled or repressed. But, to limit our consideration to the vegetable kingdom, it may be observed, that where a loose and deep soil affords an abundant supply of food, where a genial climate diffuses warmth in an adequate degree, and where a favourable exposure allows a competent access of light (for air, being fully and universally given, may be thrown out of the case); in these circumstances, a plant, if not mechanically injured, will vigorously exercise its functions, and attain the full development of its parts, thus realizing the absolute complement of life, to which it naturally tends. In the same way, when these conditions are stinted, the luxuriance of the plant is checked, in the ratio of that restraint, and the deficiency of the supply. Where any one of the external conditions is partially or inadequately supplied, the plant appears to make special, and even forced efforts to secure as much of the beneficial influence as it can, and to accommodate itself to the exigency of its situation. Thus, where light is admitted only from a single point, a plant concentrates all its powers, in stretching towards the direction of the light. Where light is shed all around, the plant throws out its branches on every side. In conformity with this principle, we find, that, in the interior of a wood, where the Trees {257} mutually impede the lateral admission of light, the tendency of each is upwards; and the consequence of this tendency is, that the plant is thereby not developed in its natural and perfect proportions, but is elongated, or drawn up to an undue height. It displays its ramification chiefly near the top; while the imperfection of its life is manifested in the whole character of its vegetation. In open exposures, on the other hand, the tree developes its existence, in full health and luxuriance. It reaches a height, such as the soil and situation admit, and sufficient to allow the branches, which are thrown out on every side, to expand their leaves freely to the sun. Not being compelled to concentrate its efforts, in securing a scanty supply of one beneficial influence, all its proportions are absolute and universal, not relative and particular. In such circumstances, therefore, it may be considered as in a full and natural state of perfection.