The contrast thus stated is stated, perhaps, with too great simplicity. The science of any history is a science of a history, that is, it is a science of natures which may themselves have a history. This fact cannot be disregarded. It is evident, therefore, that when we say that the evolution of anything discloses its history, but not its nature, we should not prejudge the possibility that there may be things the nature of which is only historically definable, the nature of which is, we may say, just their concrete history. A grain of wheat in its chemical and physical composition is a thing quite different from what we call a seed, the grain of wheat which implies what only its history can make apparent at the time of harvest. It is conceivably possible that we might know the chemical and physical composition of all seeds without any nook or corner left unexplored; that we might then be able to detect differences in their composition which would allow us to classify them with accuracy, so that one kind of seed could be distinguished without error from any other kind; and yet that we might find nothing which would indicate what the nature of those seeds is as displayed in their growth. It is considerations like this that give to vitalistic theories their recurring interest. Yet we should emphasize two things: first, that under the supposition we have made, vitalism is scientifically unnecessary; and, secondly, that vitalism would be scientifically necessary only if after fully ascertaining the composition of all seeds we were unable to distinguish between them or to classify them as of different kinds. It may well be that every living thing in its germ has a mechanical constitution as specifically and individually distinct as the specific form and individuality which its maturity reveals. The evidence points that way, and as long as it so points, vitalistic theories are naturally viewed with suspicion. No; the supposition I have ventured to make, has not been made in order that we may entertain once more a theory which retreats defeated again and again after every fresh appearance, but to emphasize the fact that the nature of a thing may be progressive. Time may enter into its substance. Our problem then becomes to discover and trace that progress, not to look for causes of it. Why should we
