To continue Reinke’s explanation: Two different classes of dominants are to be recognized. These are the operative and the formative. The former control principally the chemical activities of the organism, as when a plant turns inorganic substances into sugar, albumen, etc.; the latter are the invisible architects in the organism who control its form and structure. Both are heritable, and are capable of modification within certain limits. Closely bound up with matter and energy, they are neither matter nor energy. They can be indefinitely multiplied and (to all appearance) totally destroyed. Their multiplication does not abstract energy from other known sources, nor does their destruction restore it; they do not therefore come (visibly) under the law of the conservation of energy. They operate entirely within the framework of natural laws, and can only utilize what energies are available for them at the given time and place. Every cell has its dominants; and as an organism is a synthesis, not a mere aggregate, of cells, so its individual dominant is a synthesis of the dominants of its parts. The evolution of species, like the development of an embryo, is under the control of dominants. The conditions under which they work for this end are material and physical; these conditions can, to a great extent, be ascertained and defined, but the driving force lies beyond scientific analysis. Such is the conception of Reinke; and taken as he presents it, that is to say, merely as a kind of working hypothesis, as a means of making intelligible a vast and various mass of phenomena, it seems admirably suited to its purpose. It remains to add, though Reinke himself does not say so, that this conception of the dominants appears to harmonize remarkably with what has been put forward in regard to cell-structure and reproduction. The chromosomes are probably the material vehicles of the dominants; in fact, Weismann’s determinants seem to be the same thing under another name, though Weismann conceives them rather from the point of view of the scientist, and Reinke from that of the metaphysician. We have now arrived at an intellectual conception under which to range the phenomena (not the ultimate nature) of vital response. Let us apply it to the question of evolution. The following passage from Henslow’s Origin of Plant Structures[91] may serve to introduce this part of our discussion:—