A Criticism of the Evidence for the Mutation Theory of De Vries from the Behavior of Species of Oenothera in Crosses and in Selfed Lines

Abstract

The mutation theory of Professor De Vries rests so very largely upon deductions from his studies on species of Oenothera that any discussion of it naturally centers upon the interpretation of the behavior of these plants when selfed (in-bred) and in their crosses with one another. Of these species Oenothera Lamarckiana stands as the form most thoroughly studied with respect to its habit of throwing off in successive generations variants with numerous distinguishing characters of such a nature that they can with certainty be separated and would rank in systematic botany as clearly defined new species arising suddenly and fully formed from the parent type. Professor De Vries calls these variants 'mutants' and interprets their appearance as the spontaneous origin by mutation of new species from a plant, Oenothera Lamarckiana, which he believes to be representative of a pure species. De Vries is not willing to allow that in 0. Lamarckiana this phenomenon may be the direct result of an impure or hybrid constitution. The behavior of 0. Lamarckiana and certain other forms in this genus is, therefore, to De Vries direct experimental evidence of the origin of new species through wide and discontinuous variations, the result of spontaneous internal manifestations within the parent plants. De Vries further believes that mutations play a very important part in organic evolution and that they largely supply the material, i.e., the variations, upon which natural selection can operate. There is no question of the facts as brought out in the extensive and patient work of De Vries; they have been repeatedly confirmed. Oenothera Laimarckiana if grown in sufficiently large cultures may be expected to produce in each generation approximately the same set of 'mutants.' The proportions differ but they are apparently fairly stable for each variant; some make up about 1-2 per cent of the cultures, others are much less common. Certain of the 'mutants' breed fairly true when selfed while some are more unstable than the parent Lamarckiana. A significant feature of this performance is the clear expression of order and system in the appearance of precisely the same types through successive generations and we have no reason to suppose that 0. Lamarck-