Taking the work on Oenothera as a whole we see in it continually glimpses of order which further on are still blocked by difficulties and apparent inconsistencies. Through such a stage all the successful researches in complicated factorial analysis have passed and I see no reason for supposing that with the application of more stringent methods this more difficult set of problems will be found incapable of similar solutions. To return to the original question whether in Oenothera we can claim to see a special contemporaneous output of new species in actual process of creation, it will be obvious that while the interrelation of the several types is still so little understood, such a claim has no adequate support. It is true that many of the "mutants" of Lamarckiana can well pass for species, but this is equally true of many new combinations of pre-existing factors as we have seen in Primula Sinensis and other cases. Still less can it be admitted that these facts of uncertain import supply a justification for the conception which has played a prominent part in the scheme of the Mutationstheorie, namely that there are special periods of Mutation, when the parent-species has peculiar genetic properties. To conclude: The impression which the evidence leaves most definitely on the mind is that further discussion of the bearing which the Oenotheras may have on the problem of evolution should be postponed until we have before us the results of a searching analysis applied to a limited part of the field. In such an analysis it is to be especially remembered that we have now a new clue in the well-ascertained fact that the genetic composition of the male and female germ-cells of the same individual may be quite different. When with this possibility in view the behaviour of the types is re-examined I anticipate that many of the difficulties will be removed.
Outside the evidence from Oenothera, which, as we have seen, is still ambiguous, I know no considerable body of facts favourable to that special view of Mutation which de Vries has promulgated. Of variation, or if we will, Mutation, in respect of some one character, or resulting from recombination, there is proof in abundance; but of that simultaneous variation in several independent respects to which de Vries especially attributes the origin of new specific types I know only casual records which have yet to undergo the process of criticism.
Besides de Vries's "Mutationstheorie" and "Species and Varieties" the chief publications relating to the subject of the behaviour of Oenothera are the following: (Many other papers relating especially to the cytology of the forms have appeared.)
Davis, B. M.
Genetical Studies on Oenothera, I. Amer. Nat., XLIV, 1910, p. 108.
Genetical Studies on Oenothera, II. Ibid., XLV, 1911, p. 193.
Gates, R. R.
An Analytical Key to some of the Segregates of Oenothera.
Twentieth Annual Report of the Missouri Botanical Garden, 1909.
Studies on the Variability and Heritability of Pigmentation in Oenothera.
Ztsch. f. Abstammungslehre, 1911, IV, p. 337.
Honing, J. A.
Die Doppelnatur der Oenothera Lamarckiana.
Ztsch. f. Abstammungslehre, 1911, IV, p. 227.
Macdougal, D. T. (with A. M. Vail, G. H. Shull, and J. K. Small).
Mutants and Hybrids of the Oenotheras.
Carnegie Institution's Publication, No. 24, 1905.
Macdougal, D. T., Vail, A. M., Shull, J. H.
Mutations, Variations and Relationships of the Oenotheras.
Carnegie Institution's Publication, No. 81, 1907.
de Vries, H.
On Atavistic Variation in Oenothera cruciata.
Bull. Torrey Club, 1903, Vol. 30, p. 75.
On Twin Hybrids,
Bot. Gaz., Vol. 44, 1907, p. 401.
Ueber die Zwillingsbastarde von Oenothera nanella.
Ber. Deut. Bot. Ges., 1908, XXVI, a, p. 667.
Bastarde von Oenothera gigas. Ibid., p. 754.
On Triple Hybrids. Bot. Gaz., 1909, Vol. 47, p. 1.
Ueb. doppeltreziproke Bastarde von Oenothera biennis L. und Oenothera muricata L.
Biol. Cbltt., 1911, XXXI, p. 97.
Zeijlstra, H. H.
Oenothera nanella de Vries, eine krankhafte Pflanzenart.
Biol. Cbltt., 1911, XXXI, p. 129.
Note.
Since this chapter was written two contributions of special importance have been made to the study of the Oenothera problems. The first is that of Heribert-Nilsson.[9] The author begins by giving a critical account of the evidence for de Vries's interpretation of the nature of the mutants. In general this criticism pursues lines similar to those sketched in the foregoing chapter, concluding, as I have done, that the chief reason why factorial analysis has been declared to be inapplicable to the Oenothera mutants is because no one has hitherto set about this analysis in the right way. He has also himself made a valuable beginning of such an analysis and gives good evidential reasons for the belief that at least the red veining depends on a definite factor which also influences the size of certain parts of the plant. He argues further that many of the distinctions between the mutants are quantitative in nature. With great plausibility he suggests that the system of cumulative factors which Nilsson-Ehle discovered in the case of wheat (subsequently traced by East in regard to maize) may be operating also in these Oenotheras. According to this system several factors having similar powers may coexist in the same individual, and together produce a cumulative effect. Scope would thus be given for the production of the curious and seemingly irregular numbers so often recorded in the "mutating" families.
Another remarkable observation relating to the crosses of muricata and biennis has been published by Goldschmidt.[10] He finds that in the formation of this cross the female pronucleus takes no part in the development of the zygotic cell, but that when the male pronucleus enters, the female pronucleus is pushed aside and degenerates. As de Vries observed, the reciprocal hybrids are in each case very like the father ("stark patroklin"), a consequence which finds a natural explanation in the phenomenon witnessed by Goldschmidt. The results of the subsequent matings can also be readily interpreted on the same lines. Indications of maternal characters are nevertheless mentioned by de Vries, and if Goldschmidt's account of the cytology is confirmed, these must presumably be referred to the influence of the maternal cytoplasm. Clearly this new work opens up lines of exceptional interest. The interpretation I have offered above must probably be reconsidered. The distinction between the male and female cells of the types may no doubt be ultimately factorial, but it is difficult to regard such a distinction as created by a differential distribution of the ordinary factors.