THE plant commonwealth lies within the contours of an individual plant? rose, lily, grass, oak tree or any other. The physical features of the commonwealth have been surveyed and are well known. Notwithstanding their differences in outward aspect, all the members of the commonwealth?root, stem, leaves, and flowers?own a common plan of organisation. As the human being is the unit of a commonwealth of nations, so is the cell or protoplast the unit of the plant commonwealth. Just as certain men have the appearance of simplicity, so has the plant cell?a minute mass of nucleated cytoplasm, bounded by a solid wall of cell-wall substance, of such small dimensions that one thousand cells might lie comfortably side by side along the diameter of a penny piece. Yet, as is the case with man, the simplicity of the cell is illusory. The cell lives, feeds, respires, grows, and does many different kinds of work. Nor does it live unto itself alone. In all its manifold activities the cell influences and is influenced by other of the well-nigh innumerable cell units of the commonwealth. Indeed, the messages which by word of mouth, by post and telephone, telegraph and wireless, pass between members of our own commonwealth and leave us but little peace, are rare by comparison with those sent and received by the living cells of plants. Throughout life they are always “listening in.” In the simplest plants of all?the unicellular plants?the cell is the commonwealth. So is it in the highest (multicellular) plant at the moment of the rebirth of the individual within the ovary of the flower of the mother-plant. All plants begin life each as a single, minute mass of semi-fluid nucleated protoplasm. Every activity evinced by this living particle shows alike the diversity of its unrecognisable parts and the integrity, that is, the individuality of the whole, and throughout life diversity of activity and oneness or individuality alike persist.