these foliaceous shoots, one on another; and where, as a consequence, the first-formed of them become the main stem that acts as support to secondary and tertiary stems; they lose their green, succulent character, acquire bark, and become woody. In resuming the functions of axes they resume the structures of axes, from which they had deviated. In Fig. 71 are shown some of the leaf-like axes of _Rhipsalis rhombea_ in their young state; while Fig. 72 represents the oldest portion of the same plant, in which the foliaceous characters are quite obliterated, and there has resulted an ordinary stem-structure. One further fact is to be noted. At the same time that their leaf-like appearances are lost, the axes also lose their separate individualities. As they become stem-like, they also become integrated; and they do this so effectually that their original points of junction, at first so strongly marked, are effaced, and a consolidated trunk is produced. [Illustration: Figs. 71–72.] Joined with the facts previously specified, these facts help us to conceive how, in the evolution of flowering plants in general, the morphological components that were once distinct, may become extremely disguised. We may rationally expect that during so long a course of modification, much greater changes of form, and much more decided fusions of parts, have taken place. Seeing how, in an individual plant, the single leaves pass into compound leaves, by the development of their veins into mid-ribs while their petioles begin to simulate axes; and seeing that leaves ordinarily exhibiting definitely-limited developments, occasionally produce other leaves from their edges; we are led to suspect the possibility of still greater changes in foliar organs. When, further, we find that within the limits of one natural order, petioles usurp the functions and appearances of leaves, at the same time that in other orders, as in _Ruscus_, lateral axes so simulate leaves that their axial nature would by most not be suspected, did they not bear flowers on their mid-ribs or edges; and when, among Cactuses, we perceive that such metamorphoses and re-metamorphoses take place with great facility; our suspicion that the morphological elements of Phænogams admit of profound transformations, is deepened. And then, on discovering how frequent are the monstrosities which do not seem satisfactorily explicable without admitting the development of foliar organs into axial organs; we become ready to entertain the hypothesis that during the evolution of the phænogamic type, the distinction between leaves and axes has arisen by degrees. With our preconceptions loosened by such facts, and carrying with us the general idea which such facts suggest, let us now consider in what way the typical structure of a flowering plant may be interpreted.