It might have been expected that in the domain of plant-biology, if anywhere, the mechanistic standpoint would have been the prevailing one. For it is almost a matter of course to regard plants as devoid of sensation or “psychical” life, and as mechanical systems, chemical laboratories, and reflex mechanisms, and this way of regarding them has been made easy by the very marked uniformity and lack of spontaneity in their vital processes as compared with those of animals. But it is not the case that mechanical theories have here prevailed. The opposition to them is just as great here as elsewhere, and from the days of Wigand onwards it has been almost continuously sustained.(88) Very characteristic is Pfeffer’s “Pflanzen-Physiologie” (1897), which is written professedly from the mechanist point of view. “Vitalism,” according to this authority, is to be rejected, but instead of “vital force” he offers us “given properties,” and the alleged machine-like collocations of the most minute elements. In regard, for instance, to the riddle of development and morphogenesis, we must simply accept it as a “given property,” that the acorn grows in an oak and nothing else. The chemical explanation of the vital functions of protoplasm is also to be rejected; as a shattered watch is no longer a watch though it remains chemically the same, so it is with protoplasm. The available chemical knowledge of the substances of which protoplasm is made up is insufficient to render the vital processes intelligible. Here, as everywhere else, we have to reckon with ultimate “properties (entities), which we neither can, nor desire to analyse further.” “The human mind is no more capable of forming a conception of the ultimate cause of things than of eternity.” If all the views here indicated were followed out to their logical conclusions, they would hinder rather than further the process of reduction to terms of physico-chemical sequences. Kerner von Marilaun in his “Pflanzenleben” deliberately takes up a thorough-going vitalist position, and on this point as well as on many others he opposed the current theory of the school (Darwinism). It is true, he admits, that many of the phenomena in plants can be explained in purely mechanical terms, but they are only those which may occur also in non-living structures. The specific expressions of life cannot be explained in this way. He shows this more fully in regard to the most fundamental of all the vital processes in the plant-body—the breaking up of carbonic acid gas by the chlorophyll to obtain the carbon which is the fundamental element in all living organisms. We know the requisite conditions: the supply of raw material, and the sunlight from which the energy is derived. But how the chlorophyll makes use of these to effect the breaking up, and how it starts the subsequent syntheses of the carbon into the most complex organic compounds remains a mystery. And so on upwards through all the strictly vital phenomena.