The cambium of the Phanerogams may be regarded as the very type of a complex-equipotential system, promoting restitution of form. It runs through the whole stem of our trees, in the form of a hollow tube, placed between the inner and the outer cell-layers of the stem, and either branch or root may originate from any single one of its cells, just as circumstances require. We might call the cambium a system of the “complex” type of course, even if every one of its constituents were able to form only a root or only a branch by way of restitution. But in fact one and the same element can form both of these complex-structures; it depends only on its relative position in the actual part of the stem isolated for the purposes of experiment, what will be accomplished in every case. Here we have a state of affairs, which we shall encounter again when studying regeneration in animals: every element of the system may be said to contain potencies for the “ideal whole,” though this ideal whole will never be realised in its proper wholeness.[124] [124] The “ideal whole” is also proved to exist, if any *given* “Anlage,” say of a branch, is forced to give origin to a root, as has really been observed in certain plants. This case, like many other less extreme cases of what might be called “compensatory heterotypy,” are best to be understood by the aid of the concept of “prospective potency.” It is very misleading to speak of a metamorphosis here. I fully agree with Krašan about this question. See also page 112, note 1, and my *Organ. Regul.* pp. 77, 78. But there is no need to recur to the “ideal whole” in many other cases of adventitious restitution in plants. On isolated leaves of the well-known begonia, a whole plant, containing all the essential parts, may arise from any single cell[125] of the epidermis, at least along the veins, and in some liverworts it has been shown by Vöchting, that almost every cell of the whole is able to reproduce the plant, as is also the case in many algae. [125] Winkler has discovered the important fact, that the adventitious buds formed upon leaves may originate either from one single cell of the epidermis or from several cells together; a result that is very important with respect to the problem of the distribution of “potencies.”