We only, I believe, can state the fact that there *are* relations between morphogenetic causes and effects which *are* adaptations, that functional disturbances or changes are followed by single histogenetic reactions from the organism, which are compensations of its disturbed or changed functional state. We are speaking of facts here, of very strange ones indeed. But I feel unable to formulate a real proof against all sorts of mechanism out of these facts: there *might* be a machine, to which all is due in a pre-established way. Of course we should hardly regard such a machine as very probable, after we have seen that it *cannot* exist in other fields of morphogenesis. But we are searching for a new and independent proof; and that is indeed not to be found here.[88] [88] The “secondary adaptations” observed by Vöchting are too complicated and too much mingled with restitutions to allow any definite analysis of the fact of the “secondary adaptation” as such. At present it must be taken as one of the fundamental *facts* of the organogenetic harmony, that the cells of functioning tissues do possess the faculty of reacting to factors which have changed the state of functioning, in a way which normalises this state histologically. And it is a fact also that even cells, which are not yet functioning but are in the so-called embryonic or indifferent condition contributing to the physiological completion of the tissue, react to factors embracing new functional conditions of the whole in a manner which leads to an adaptation of that whole to those conditions. This is a very important point in almost all morphological adaptation, whether corresponding to functional changes from without or resulting from the very nature of functioning. In fact, such cells as have already finished their histogenesis are, as a rule, only capable of changing their size adaptively, but are not able to divide into daughter-cells or to change their histological qualities fundamentally; in technical terms, they can only assist “hypertrophy” but not “hyperplasia.” Any adaptive change of a tissue therefore, that implies an increase in the number of cellular elements or a real process of histogenesis, has to start from “indifferent” cells, that is to say, cells that are *not yet* functioning in the form that is typical of the tissue in question; and, strange to say, these “embryonic” cells--*i.e.* the “cambium” in higher plants and many kinds of cells in animals--*can* do what the functional state requires. It is to be hoped that future investigations will lay a greater stress upon this very important feature of all adaptation. 2. PHYSIOLOGICAL ADAPTATION[89]