In the test conditions of his own garden, in an experiment covering thirteen years, he observed over fifty thousand of the Lamarckiana spread over eight generations and of these eight hundred were mutations divided among seven new elementary species. These mutations, when self-fertilized, or fertilized from plants like themselves, bred true to themselves, thus answering the test of a real species. DeVries also watched the field from which his original forms were taken, and saw that similar mutations occurred there so that they were not in any way due to cultivation.
Thus has the modest mutating primrose contributed its quota to the solution of that riddle of the universe which, until it is solved, will always command a paramount position in the thoughts of men.
DeVries discourages the notion that mutations are always occurring everywhere, which might seem to be one of the inferences from his theory, and his twenty-fourth lecture of the series, delivered before the University of California is entitled “The Hypothesis of Periodic Mutations.” The common primrose, he says, seems to be immutable at present, and argues that it must have had a mutatory period sometime in the past, when, perhaps, the evening primrose was not mutating. He says: “All the facts point to the conclusion that these periods, of stability and mutability, alternate more or less regularly with one another.”
He deals the Neo-Lamarckians a heavy blow by his denial of “direct” adaptation, and he greatly strengthens their opponents when he asserts that mutation takes place, not only in useful directions, but in all directions, leaving natural selection to destroy the unfit. This is a restatement of Darwin’s conception, followed by Weismann, of “fortuitous” variations, and is contrary to the notion of Spencer and Haeckel, that variations are mainly in the direction of adaptation to environment, as a result of animals exerting themselves in that direction.
This point is well stated by DeVries in the following passage,--“This failure of a large part of the productions of nature deserves to be considered at some length. It may be elevated to a principle, and may be made use of to explain many difficult points of the theory of descent. If in order to secure one good novelty nature must produce ten or twenty or perhaps more bad ones at the same time, the possibility of improvements coming by pure chance must be granted at once. All hypotheses concerning the direct causes of adaptation at once become superfluous, and the great principle enunciated by Darwin once more reigns supreme.”