Beings, in which life alone is added to gravitation and etherodynamy constitute the _Vegetable Kingdom_. Now there is one general fact displayed by this group, the significance of which has not, it seems to me, been sufficiently understood. With the exception of certain phenomena of _unconscious irritability_ which have long been known in some plants of a superior order, and of facts, probably of the same class, which have been established chiefly with reference to some reproductive organs of plants of an inferior order, every movement which takes place in plants appears to be produced _solely_ by inanimate forces. The transfer of matter in particular, which is necessary for the development and sustenance of every vegetable, belongs to actions of this kind. Can we believe that these forces, as they are known to us from innumerable experiments, could, if left to themselves, have formed an oak, or even raised a mushroom? Can we believe that they could have _organised_ the acorn or the spore, and hidden in those minute bodies the power of reproducing the parent? And yet without them the vegetable cannot exist. But, in my opinion, nothing makes their real subordination more apparent than the importance of their part in the process of execution. They may be compared to workmen raising an edifice under the eye of the architect who has made the plan. Are we then to conclude that life is an intelligent force, conscious of the part it plays, and enjoying the dominion it exercises over the subordinate inanimate forces? Not at all. Like these forces, it is ruled by general and fixed laws. Nevertheless, we do not find in the application of these laws, and in the results to which they lead, the mathematical precision of the laws and phenomena of gravitation and etherodynamy. Their mode of action merely seems to oscillate between limits which remain impassable. This kind of liberty, and the bounds imposed upon it, are conspicuous in the constant diversity of the products of life, a diversity which contrasts in so striking a manner with the uniformity of the products of etherodynamy. Crystals, when similar in composition, and when formed under similar circumstances, resemble each other perfectly; but we never find two leaves exactly alike upon the same tree. The vegetable kingdom is, therefore, characterised by _three kinds of phenomena_: _the Keplerian movement_, _physico-chemical phenomena_, and _vital phenomena_, which may be ascribed to the action of three forces: _Gravitation_, _Etherodynamy_, and _Life_.