The facts at the present time generally accepted regarding the ultimate composition, and the sources of the constituents, of plants, have, for the most part, received their preponderating weight of proof within the limits of the present century. But it is to the century preceding it that we must look for the establishment of much that was essential as the foundation of those advances which have since been made. Whatever may be the value at present attached to the particular views of Hales regarding the composition and the sources of vegetable matter, we must accord to his labours, in the early part of the eighteenth century, the merit of having been guided by a proper spirit of experimental inquiry. Nor did he fail in applying to good account, and even in extending, the then existing knowledge of the material things around him which were apparently involved in the mysterious processes of vegetable growth.