BIBLIOGRAPHY.

1.Correns, C. G.Mendel’s Regel über das Verhalten der Nachkommenschaft der Rassenbastarde,Ber. deut. bot. Ges.,XVIII., 1900, p. 158.2. —— Gregor Mendel’s “Versuche über Pflanzen-Hybriden” und die Bestätigung ihrer Ergebnisse durch die neuesten Untersuchungen,Bot. Ztg., 1900, p. 229.3. —— Ueber Levkoyenbastarde zur Kenntniss der Grenzen der Mendel’schen Regeln,Bot. Cblt., 1900, Vol.LXXXIV., p. 97.4. —— Bastarde zwischen Maisrassen, mit besonderer Berücksichtigung der Xenien,Bibliotheca Botanica, Hft. 53, 1901.5.Crampe.Kreuzungen zwischen Wanderratten verschiedener Farbe,Landwirths. Jahrb.,VI., 1877, p. 384.6. —— Zucht-Versuche mit zahmen Wanderratten. 1. Resultate der Zucht in Verwandtschaft,ibid.,XII., 1883, p. 389. 2. Resultate der Kreuzung der zahmen Ratten mit wilden,ibid.,XIII., 1884, p. 699.7. —— Die Gesetze der Vererbung der Farbe,ibid.,XIV., p. 539.8.Darwin, C.Variation of Animals and Plants under Domestication, ed. 2,I., pp. 348 and 428.9.Fischer, Johann von.Die Säugethiere des StPetersburger Gouvernements,Zool. Garten,X., 1869, p. 336.10. —— Iltis (Mustela putorius) und Frett (Mustela furo),ibid.,XIV., 1873, p. 108.11.Fischer, Johann von.Beobachtungen über Kreuzungen verschiedener Farbenspielarten innerhalb einer Species,ibid.,XV., 1874, p. 361.12.Focke, W. O.Die Pflanzen-Mischlinge, Bornträger, Berlin, 1881.13. —— Ueber dichotype Gewächse.Oesterr. bot. Ztschr.,XVIII., 1868, p. 139.14.Galton, F.Natural Inheritance, Macmillan and Co., London, 1889.15. —— The Average Contribution of each several Ancestor to the total Heritage of the Offspring,Proc. Roy. Soc.,LXI., 1897, p. 401.16.Gärtner, C. F. von.Versuche und Beobachtungen über die Bastarderzeugung im Pflanzenreich, Stuttgart, 1849.17.Gitay, E.Ueber den directen Einfluss des Pollens auf Frucht- und Samenbildung,Pringsheim’s JB. d. wiss. Bot.,XXV., 1893, p. 489.18.Godron, D. A.Des Hybrides Végétaux, etc.Ann. Sci. Nat. Bot., Ser. 4,XIX., 1863, p. 135, and a series of papers inMém. Acad. Stanislas, Nancy, 1864, 1865, and especially 1872.19.Guaita, G. von.Versuche mit Kreuzungen von verschiedenen Rassen der Hausmaus,Ber. d. naturf. Ges. Freiburg,X., 1898, p. 317.20. —— Zweite Mittheilung, etc.,ibid.,XI., 1900, p. 131.21.Knight, T. A.An account of some experiments on the Fecundation of Vegetables,Phil. Trans., 1799, Pt.II., p. 195.122.Küster, E.Die Mendel’schen Regeln, ihre ursprüngliche Fassung und ihre moderne Ergänzungen,Biol. Cblt.,XXII., 1902, p. 129.23.Laxton, T.Observations on the variations effected by crossing in the colour and character of the seed of Peas,Internat. Hort. Exhib. and Bot. Congr., Report, 1866, p. 156.24. —— Notes on some Changes and Variations in theOffspring of Cross-fertilized Peas,Jour. Hort. Soc., N.S.III., 1872, p. 10.25.Laxton, T.Improvement amongst Peas,Jour. Hort. Soc., 1890,XII., 1, p. 29.26.Mendel, Gregor Johann.Versuche über Pflanzen-Hybriden,Verh. naturf. Ver. in Brünn, BandIV., 1865,Abhandlungen, p. 1; reprinted inFlora, 1901, and in Ostwald’sKlassiker d. exakten Wiss.English translation inJour. R. Hort. Soc., 1901,XXVI.27. —— Ueber einige aus künstlicher Befruchtung gewonnenen Hieracium-Bastarde,ibid.,VIII., 1869,Abhandlungen, p. 26.28.Millardet.Note sur l’hybridation sans croisement, ou fausse hybridation,Mém. Soc. Sci. Bordeaux, Ser. 4,IV., 1894, p. 347.29.C. Naudin.Nouvelles recherches sur l’Hybridité dans les Végétaux,Nouv. Arch. Mus.,I., 1865, p. 25.30. ——Ann. sci. nat., Bot., Ser. 4,XIX., p. 180.31.Pearson, Karl.On the Law of Ancestral Heredity,Proc. Roy. Soc.,LXII., 1898, p. 386.32. —— On the Law of Reversion,ibid.,LXVI., 1900, p. 140.33. ——The Grammar of Science, second edition, London, A. and Charles Black, 1900.34. —— Mathematical Contributions to the Theory of Evolution. VIII. On the Inheritance of Characters not capable of exact Measurement,Phil. Trans. Roy. Soc., 1900, Vol. 195, p. 79.35.Rimpau.Kreuzungsprodukte landw. Kulturpflanzen,Landw. Jahrb.,XX., 1891.36.Tschermak, E.Ueber künstliche Kreuzung beiPisum sativum,Ztschrft. f. d. landwirths. Versuchswesen in Oesterr., 1900,III., p. 465.37. —— Weitere Beiträge über Verschiedenwerthigkeit der Merkmale bei Kreuzung von Erbsen and Bohnen,ibid., 1901,IV., 641;abstract in Ber. deut. bot. Ges., 1901,XIX., p. 35.38.Tschermak, E.Ueber Züchtung neuer Getreiderassen mittelst künstlicher Kreuzung,ibid., 1901,IV., p. 1029.39.Vilmorin-Andrieux and Co.Les Plantes Potagères, 1st ed. 1883; 2nd ed. 1891.40.Vries, H. de.Sur la loi de disjonction des hybrides,Comptes Rendus, 26 March, 1900.41. —— Das Spaltungsgesetz der Bastarde,Ber. deut. bot. Ges., 1900,XVIII., p. 83.42. —— Ueber erbungleiche Kreuzungen,ibid., p. 435.43. —— Sur les unités des caractères spécifiques et leur application à l’étude des hybrides,Rev. Gén. de Bot., 1900,XII., p. 257. See also by the same author,Intracellulare Pangenesis, Jena, 1889, in which the conception of unit-characters is clearly set forth.44. ——Die Mutationstheorie, Vol.I., Leipzig, 1901.45.Weldon, W. F. R.Mendel’s Laws of Alternative Inheritance in Peas,Biometrika,I., Pt. ii., 1902, p. 228.46.Wichura, Max.Die Bastardbefruchtung im Pflanzenreich, erläutert an den Bastarden der Weiden, Breslau, 1865.

1.Correns, C. G.Mendel’s Regel über das Verhalten der Nachkommenschaft der Rassenbastarde,Ber. deut. bot. Ges.,XVIII., 1900, p. 158.

2. —— Gregor Mendel’s “Versuche über Pflanzen-Hybriden” und die Bestätigung ihrer Ergebnisse durch die neuesten Untersuchungen,Bot. Ztg., 1900, p. 229.

3. —— Ueber Levkoyenbastarde zur Kenntniss der Grenzen der Mendel’schen Regeln,Bot. Cblt., 1900, Vol.LXXXIV., p. 97.

4. —— Bastarde zwischen Maisrassen, mit besonderer Berücksichtigung der Xenien,Bibliotheca Botanica, Hft. 53, 1901.

5.Crampe.Kreuzungen zwischen Wanderratten verschiedener Farbe,Landwirths. Jahrb.,VI., 1877, p. 384.

6. —— Zucht-Versuche mit zahmen Wanderratten. 1. Resultate der Zucht in Verwandtschaft,ibid.,XII., 1883, p. 389. 2. Resultate der Kreuzung der zahmen Ratten mit wilden,ibid.,XIII., 1884, p. 699.

7. —— Die Gesetze der Vererbung der Farbe,ibid.,XIV., p. 539.

8.Darwin, C.Variation of Animals and Plants under Domestication, ed. 2,I., pp. 348 and 428.

9.Fischer, Johann von.Die Säugethiere des StPetersburger Gouvernements,Zool. Garten,X., 1869, p. 336.

10. —— Iltis (Mustela putorius) und Frett (Mustela furo),ibid.,XIV., 1873, p. 108.

11.Fischer, Johann von.Beobachtungen über Kreuzungen verschiedener Farbenspielarten innerhalb einer Species,ibid.,XV., 1874, p. 361.

12.Focke, W. O.Die Pflanzen-Mischlinge, Bornträger, Berlin, 1881.

13. —— Ueber dichotype Gewächse.Oesterr. bot. Ztschr.,XVIII., 1868, p. 139.

14.Galton, F.Natural Inheritance, Macmillan and Co., London, 1889.

15. —— The Average Contribution of each several Ancestor to the total Heritage of the Offspring,Proc. Roy. Soc.,LXI., 1897, p. 401.

16.Gärtner, C. F. von.Versuche und Beobachtungen über die Bastarderzeugung im Pflanzenreich, Stuttgart, 1849.

17.Gitay, E.Ueber den directen Einfluss des Pollens auf Frucht- und Samenbildung,Pringsheim’s JB. d. wiss. Bot.,XXV., 1893, p. 489.

18.Godron, D. A.Des Hybrides Végétaux, etc.Ann. Sci. Nat. Bot., Ser. 4,XIX., 1863, p. 135, and a series of papers inMém. Acad. Stanislas, Nancy, 1864, 1865, and especially 1872.

19.Guaita, G. von.Versuche mit Kreuzungen von verschiedenen Rassen der Hausmaus,Ber. d. naturf. Ges. Freiburg,X., 1898, p. 317.

20. —— Zweite Mittheilung, etc.,ibid.,XI., 1900, p. 131.

21.Knight, T. A.An account of some experiments on the Fecundation of Vegetables,Phil. Trans., 1799, Pt.II., p. 195.

122.Küster, E.Die Mendel’schen Regeln, ihre ursprüngliche Fassung und ihre moderne Ergänzungen,Biol. Cblt.,XXII., 1902, p. 129.

23.Laxton, T.Observations on the variations effected by crossing in the colour and character of the seed of Peas,Internat. Hort. Exhib. and Bot. Congr., Report, 1866, p. 156.

24. —— Notes on some Changes and Variations in theOffspring of Cross-fertilized Peas,Jour. Hort. Soc., N.S.III., 1872, p. 10.

25.Laxton, T.Improvement amongst Peas,Jour. Hort. Soc., 1890,XII., 1, p. 29.

26.Mendel, Gregor Johann.Versuche über Pflanzen-Hybriden,Verh. naturf. Ver. in Brünn, BandIV., 1865,Abhandlungen, p. 1; reprinted inFlora, 1901, and in Ostwald’sKlassiker d. exakten Wiss.English translation inJour. R. Hort. Soc., 1901,XXVI.

27. —— Ueber einige aus künstlicher Befruchtung gewonnenen Hieracium-Bastarde,ibid.,VIII., 1869,Abhandlungen, p. 26.

28.Millardet.Note sur l’hybridation sans croisement, ou fausse hybridation,Mém. Soc. Sci. Bordeaux, Ser. 4,IV., 1894, p. 347.

29.C. Naudin.Nouvelles recherches sur l’Hybridité dans les Végétaux,Nouv. Arch. Mus.,I., 1865, p. 25.

30. ——Ann. sci. nat., Bot., Ser. 4,XIX., p. 180.

31.Pearson, Karl.On the Law of Ancestral Heredity,Proc. Roy. Soc.,LXII., 1898, p. 386.

32. —— On the Law of Reversion,ibid.,LXVI., 1900, p. 140.

33. ——The Grammar of Science, second edition, London, A. and Charles Black, 1900.

34. —— Mathematical Contributions to the Theory of Evolution. VIII. On the Inheritance of Characters not capable of exact Measurement,Phil. Trans. Roy. Soc., 1900, Vol. 195, p. 79.

35.Rimpau.Kreuzungsprodukte landw. Kulturpflanzen,Landw. Jahrb.,XX., 1891.

36.Tschermak, E.Ueber künstliche Kreuzung beiPisum sativum,Ztschrft. f. d. landwirths. Versuchswesen in Oesterr., 1900,III., p. 465.

37. —— Weitere Beiträge über Verschiedenwerthigkeit der Merkmale bei Kreuzung von Erbsen and Bohnen,ibid., 1901,IV., 641;abstract in Ber. deut. bot. Ges., 1901,XIX., p. 35.

38.Tschermak, E.Ueber Züchtung neuer Getreiderassen mittelst künstlicher Kreuzung,ibid., 1901,IV., p. 1029.

39.Vilmorin-Andrieux and Co.Les Plantes Potagères, 1st ed. 1883; 2nd ed. 1891.

40.Vries, H. de.Sur la loi de disjonction des hybrides,Comptes Rendus, 26 March, 1900.

41. —— Das Spaltungsgesetz der Bastarde,Ber. deut. bot. Ges., 1900,XVIII., p. 83.

42. —— Ueber erbungleiche Kreuzungen,ibid., p. 435.

43. —— Sur les unités des caractères spécifiques et leur application à l’étude des hybrides,Rev. Gén. de Bot., 1900,XII., p. 257. See also by the same author,Intracellulare Pangenesis, Jena, 1889, in which the conception of unit-characters is clearly set forth.

44. ——Die Mutationstheorie, Vol.I., Leipzig, 1901.

45.Weldon, W. F. R.Mendel’s Laws of Alternative Inheritance in Peas,Biometrika,I., Pt. ii., 1902, p. 228.

46.Wichura, Max.Die Bastardbefruchtung im Pflanzenreich, erläutert an den Bastarden der Weiden, Breslau, 1865.

Received as this sheet goes to press:—

Correns, C.Die Ergebnisse der neuesten Bastardforschungen für die Vererbungslehre,Ber. deut. bot. Ges.,XIX., Generalversammlungs-Heft 1.—— Ueber den Modus und den Zeitpunkt der Spaltung der Anlagen bei den Bastarden vom Erbsen-Typus,Bot. Ztg., 1902, p. 65.

Correns, C.Die Ergebnisse der neuesten Bastardforschungen für die Vererbungslehre,Ber. deut. bot. Ges.,XIX., Generalversammlungs-Heft 1.

—— Ueber den Modus und den Zeitpunkt der Spaltung der Anlagen bei den Bastarden vom Erbsen-Typus,Bot. Ztg., 1902, p. 65.

FOOTNOTES:1Biometrika,I., 1902, Pt.II.2Biometrika,I.Pt.I.p. 5.3The first half of this paper is reprinted with additions and modifications from theJournal of the Royal Horticultural Society, 1900, vol.XXV., parts 1 and 2. Written almost immediately after the rediscovery of Mendel, it will be seen to be already in some measure out of date, but it may thus serve to show the relation of the new conceptions to the old.4See later. Galton gave a simple diagrammatic representation of his law inNature, 1898, vol.LVII.p. 293.5These we now recognize as examples of Mendelian ‘dominance.’6Comptes Rendus, March 26, 1900, andBer. d. Deutsch. Bot. Ges.xviii. 1900, p. 83.7This conception of discontinuity is of course pre-Mendelian.8‘Versuche üb. Pflanzenhybriden’ in theVerh. d. Naturf. Ver. Brünn, iv. 1865.9Note that by these novel terms the complications involved by use of the expression “prepotent” are avoided.10Professor Weldon (p. 232) takes great exception to this statement, which he considerately attributes to “some writers.” After examining the conclusions he obtained by algebraical study of Mendel’s figures I am disposed to think my statement not very far out.11See later.12Tschermak’s investigations were besides directed to a re-examination of the question of the absence of beneficial results on cross-fertilisingP. sativum, a subject already much investigated by Darwin, and upon this matter also important further evidence is given in great detail.13For simplicity the case of self-fertilisation is omitted from this consideration.14In all the cases discussed it is assumed that the gametes are similar except in regard to the “heritage” they bear, and that nooriginalvariation is taking place. The case of mosaics is also left wholly out of account (see later).15The term “gamete” is now generally used as the equivalent of “germ-cell,” whether male or female, and the term “zygote” is here used for brevity to denote the organism resulting from fertilisation.16In Pearson’s modification the parents contribute 0·3, the grandparents 0·15, the great-grandparents ·075.17See the works referred to above.18This conception was clearly formed by Naudin simultaneously with Mendel, but it was not worked out by him and remained a mere suggestion. In one place also Focke came very near to the same idea (see Bibliography).19See von Guaita,Ber. naturf. Ges. FreiburgX. 1898 and XI. 1899, quoted by Professor Weldon (see later).20This fact sufficiently indicates the difficulties involved in a superficial treatment of the phenomenon of reversion. To call such reversions as those named above “returns to ancestral type” would be, if more than a descriptive phrase were intended, quite misleading. It is not the ancestraltypethat has come back, but something else has come in its guise, as the offspring presently prove. For the first time we thus begin to get a rationale of “reversion.”21It will be understood from what follows, that the existence of mosaic zygotes is noproofthat either component gamete was mosaic.22A few additional particulars are given in Tschermak’s edition.23[This translation was made by the Royal Horticultural Society, and is reprinted with modifications and corrections, by permission. The original paper was published in theVerh. naturf. Ver. in Brünn, Abhandlungen,IV.1865, which appeared in 1866.]24[It is to the clear conception of these three primary necessities that the whole success of Mendel’s work is due. So far as I know this conception was absolutely new in his day.]25[Mendel uses the terms “albumen” and “endosperm” somewhat loosely to denote the cotyledons, containing food-material, within the seed.]26One species possesses a beautifully brownish-red coloured pod, which when ripening turns to violet and blue. Trials with this character were only begun last year. [Of these further experiments it seems no account was published. Correns has since worked with such a variety.]27[This is often called the Mummy Pea. It shows slight fasciation. The form I know has white standard and salmon-red wings.]28[In my account of these experiments (R.H.S. Journal, vol. xxv. p. 54) I misunderstood this paragraph and took “axis” to mean thefloralaxis, instead of the main axis of the plant. The unit of measurement, being indicated in the original by a dash (′), I carelessly took to have been aninch, but the translation here given is evidently correct.]29[It is somewhat surprising that no mention is made of Thrips, which swarm in Pea flowers. I had come to the conclusion that this is a real source of error and I see Laxton held the same opinion.]30[This also happens in Sweet Peas.]31[Mendel throughout speaks of his cross-bred Peas as “hybrids,” a term which many restrict to the offspring of two distinctspecies. He, as he explains, held this to be only a question of degree.]32[Note that Mendel, with true penetration, avoids speaking of the hybrid-character as “transmitted” by either parent, thus escaping the error pervading modern views of heredity.]33[Gärtner, p. 223.]34[It is much to be regretted that Mendel does not give the complete series individually. No one who repeats such experiments should fail to record theindividualnumbers, which on seriation are sure to be full of interest.]35[This paragraph presents the view of the hybrid-character as something incidental to the hybrid, and not “transmitted” to it—a true and fundamental conception here expressed probably for the first time.]36[This statement of Mendel’s in the light of present knowledge is open to some misconception. Though his work makes it evident that such varieties may exist, it is very unlikely that Mendel could have had seven pairs of varieties such that the members of each pair differed from each other inonlyone considerable character (wesentliches Merkmal). The point is probably of little theoretical or practical consequence, but a rather heavy stress is thrown on “wesentlich.”]37[Note that Mendel does not state the cotyledon-colour of the first crosses in this case; for as the coats were thick, it could not have been seen without opening or peeling the seeds.]38[“False hybridism” was of course unknown to Mendel.]39[This and the preceding paragraph contain the essence of the Mendelian principles of heredity.]40[To prove, namely, that both were similarly differentiated, and not one or other only.]41[Whether segregation by such units is more than purely fortuitous could probably be determined by seriation.]42[In the original the sign of equality (=) is here represented by +, evidently a misprint.]43[This is the only passage where Mendel can be construed as asserting universal dominance forPisum; and even here, having regard to the rest of the paper, it is clearly unfair to represent him as predicating more than he had seen in his own experiments. Moreover in flower and seed-coat colour (which is here meant), using his characters dominance must be almost universal, if not quite.]44[It appears to me clear that this expression is incorrectly given, and the argument regarding compound characters is consequently not legitimately developed. The original compound character should be represented asA1A2A3. . . which when fertilised bya1givesA1A2A3. . . a as the hybrid of the first generation. Mendel practically tells us these were all alike, and there is nothing to suggest that they were diverse. When on self-fertilisation, they break up, they will produce the gametes he specifies; but they may also produceA1A1andA2A2,A1A2a, &c., thereby introducing terms of a nature different from any indicated by him. That this point is one of the highest significance, both practical and theoretical, is evident at once.]45[It seems very doubtful if the zygotes are correctly represented by the termsA1aA2a,A2aa,A1aa; for in the hybridsA1a, &c. the allelomorphsA1anda, &c. should by hypothesis be separated in the gametes.]46InPisumit is placed beyond doubt that for the formation of the new embryo a perfect union of the elements of both fertilising cells must take place. How could we otherwise explain that among the offspring of the hybrids both original types reappear in equal numbers and with all their peculiarities? If the influence of the egg cell upon the pollen cell were only external, if it fulfilled therôleof a nurse only, then the result of each artificial fertilisation could be no other than that the developed hybrid should exactly resemble the pollen parent, or at any rate do so very closely. This the experiments so far have in no wise confirmed. An evident proof of the complete union of the contents of both cells is afforded by the experience gained on all sides that it is immaterial, as regards the form of the hybrid, which of the original species is the seed parent or which the pollen parent.47“Welche in den Grundzellen derselben in lebendiger Wechselwirkung stehen.”48“Dem einzelnen Beobachter kann leicht ein Differenziale entgehen.”49[The argument of these two last paragraphs appears to be that though the general mutability of natural species might be doubtful, yet among cultivated plants the transference of characters may be accomplished, and may occur by integral steps until one species is definitely “transformed” into the other.]50[Published inVerh. naturf. Ver. Brünn, Abhandlungen,VIII. 1869, p. 26, which appeared in 1870.]51The plant used in this experiment is not exactly the typicalH. echioides. It appears to belong to the series transitional toH. præaltum, but approaches more nearly toH. echioidesand for this reason was reckoned as belonging to the latter.52The words “general” and “universal” appear to be used by Professor Weldon as interchangeable. Cp. Weldon, p. 235 and elsewhere, with Abstract given below.53These words occur p. 252: “The fundamental mistake which vitiates all work based upon Mendel’s method is the neglect of ancestry, and the attempt to regard the whole effect upon offspring produced by a particular parent, as due to the existence in the parent of particular structural characters, &c.” As a matter of fact the view indicated in these last words is especially repugnant to the Mendelian principle, as will be seen.54I greatly regret that I have not a precise understanding of the basis of the modification proposed by Pearson. His treatment is in algebraical form and beyond me. Nevertheless I have every confidence that the arguments are good and the conclusion sound. I trust it may not be impossible for him to provide the non-mathematical reader with a paraphrase of his memoir. The arithmetical differences between the original and the modified law are of course clear.55I have searched Professor Pearson’s paper in vain for any considerable reservation regarding or modification of this general statement. Professor Pearson enuntiates the law as “only correct on certain limiting hypotheses,” but he declares that of these the most important is “the absence of reproductive selection, i.e. the negligible correlation of fertility with the inherited character, and the absence of sexual selection.” The case of in-and-in breeding is also reserved.56K. Pearson,Grammar of Science, 2nd ed. 1900, p. 36.57Grammar of Science, 2nd ed. 1900, p. 480.58Phil. Trans.1900, vol. 195, A, p. 121.59“If this be done, we shall, I venture to think, keep not only our minds, but our points for observation, clearer; and further, the failure of Mr Galton’s statement in the one case will not in the least affect its validity in the other.” Pearson (32), p. 143.60Grammar of Science, 1900, p. 494. See also Pearson,Proc. Roy. Soc.1900,LXVI.pp. 142–3.61On an average of cases, in equal numbers, as Mendel found.62Read in this connexion Pearson, K.,Grammar of Science, 2nd ed. 1900, pp. 390–2.Professor Weldon even now opens his essay with the statement—or perhaps reminiscence—that “it is perfectly possible and indeed probable that the difference between these forms of inheritance [blended, mosaic, and alternative] is only one of degree.” This may be true; but reasoning favourable to this proposition could equally be used to prove the difference between mechanical mixture and chemical combination to be a difference of degree.63The whole question as to seed-coat colour is most complex. Conditions of growth and ripening have a great effect on it. Mr Arthur Sutton has shown me samples ofNe Plus Ultragrown in England and abroad. This pea has yellow cotyledons with seed-coats either yellow or “blue.” The foreign sample contained a much greater proportion of the former. He told me that generally speaking this is the case with samples ripened in a hot, dry climate.Unquestionable Xenia appears occasionally, and will be spoken of later. Moreover to experiment with such aplant-character an extra generation has to be sown and cultivated. Consequently the evidence is meagre.64Knowing my interest in this subject Professor Weldon was so good as to forward to me a series of his peas arranged to form a scale of colours and shapes, as represented in his Plate I. I have no doubt that the use of such colour-scales will much facilitate future study of these problems.65I notice that Vilmorin in the well-knownPlantes Potagères, 1883, classifies the intermediate-coloured peas with thegreen.66Similarly thoughtallanddwarfare Mendelian characters, peas occur of all heights and are usually classified as tall, half-dwarfs, and dwarfs.67Wrinkling must of course be distinguished further from the squaring due to the peas pressing against each other in the pod.In connexion with these considerations I may mention that Vilmorin makes the interesting statement that most peas retain their vitality three years, dying as a rule rapidly after that time is passed, though occasionally seeds seven or eight years old are alive; but thatwrinkledpeas germinate as a rule less well than round, and do not retain their vitality so long as the round. Vilmorin-Andrieux,Plantes Potagères, 1883, p. 423. Similar statements regarding the behaviour of wrinkled peas in India are made by Firminger,Gardening for India, 3rd ed. 1874, p. 146.68Cotyledon-colour is not nearly so sensitive to ordinary changes in conditions as coat-colour, provided the coat be uninjured. But even in monomorphicgreenvarieties, a seed which for any cause has burst on ripening, has the exposed parts of its cotyledonsyellow. The same may be the case in seeds of green varieties injured byBruchusor birds. These facts make one hesitate before denying the effects of conditions on the cotyledon-colour even of uninjured seeds, and the variation described above may have been simply weathering. The seeds were gathered very late and many were burst inLaxton’s Alpha. I do not yet know they are alive.69It is interesting to see that in at least one case the same—or practically the same—variety has been independently produced by different raisers, as we now perceive, by the fortuitous combination of similar allelomorphs.Sutton’s RingleaderandCarter’s First Crop(and two others) are cases in point, and it is peculiarly instructive to see that in the discussion of these varieties when they were new, one of the points indicating their identity was taken to be the fact that they producedthe same “rogues.”SeeGard. Chron.1865, pp. 482 and 603; 1866, p. 221; 1867, pp. 546 and 712.Rimpau quotes Blomeyer (Kultur der Landw. Nutzpflanzen, Leipzig, 1889, pp. 357 and 380) to the effect thatpurple-flowered plants withwrinkledseeds may spring as direct sports from peas withwhiteflowers androundseeds. I have not seen a copy of Blomeyer’s work. Probably this “wrinkling” was “indentation.”70The asymmetries here conceived may of course be combined in an inclusive symmetry. Till the differentiation can be optically recognized in the gametes we shall probably get no further with this part of the problem.71Materials for the Study of Variation, 1894, p. 78.72The varieties used wereExpress,Laxton’s Alpha,Fillbasket,McLean’s Blue Peter,Serpette nain blanc,British Queen,très nain de Bretagne, Sabre,mange-toutDebarbieux, and a large “grey” sugar-pea,pois sans parchemin géant à très large cosse. Not counting the last two, five are round and three are wrinkled. As to cotyledons, six have yellow and four have green. In about 80 crosses I saw no exception to dominance of yellow; but one apparently clear case of dominance of wrinkled and some doubtful ones.73Professor Weldon may take this as a famous blow for Mendel, till he realizes what is meant by Mendel’s “Hybrid-character.”74In addition to those spoken of later, where the great difference between reciprocals is due to thematernalcharacters of the seeds.75I have not here considered the case in which male and female elements of a pure variety are not homologous and the variety is apermanentmonomorphic “mule.” Such a phenomenon, when present, will prove itself in reciprocal crossing. I know no such case in peas for certain.76It will be understood that a “mule” form is quite distinct from what is generally described as a “blend.” One certain criterion of the “mule” form is the fact that it cannot be fixed, see p. 25. There is little doubt that Laxton had such a “mule” form when he speaks of “the remarkably fine but unfixable pea, Evolution.”J. R. Hort. Soc.XII.1890, p. 37 (v. infra).77Using the word metaphorically.78“Ueber die Blüthezeit der Hybriden sind die Versuche noch nicht abgeschlossen. So viel kann indessen schon angegeben werden, dass dieselbe fast genau in der Mitte zwischen jener der Samen- und Pollenpflanze steht, und die Entwicklung der Hybriden bezüglich dieses Merkmales wahrscheinlich in der nämlichen Weise erfolgt, wie es für die übrigen Merkmale der Fall ist.” Mendel, p. 23.79As has been already shown the discovery could have been made equally well and possibly with greater rapidity in a case in which the hybrid had a character distinct from either parent. The cases that wouldnothave given a clear result are those where there is irregular dominance of one or other parent.80Weldon, p. 240.81See p. 43.82In some transparent coats there is pigment, but so little as a rule that xenia would be scarcely noticeable.83Usually correlated characters, as Mendel knew.84Animals and Plants, 2nd ed. 1885, p. 428.85“Eine andere Frage ist jedoch, ob der Einfluss des Pollens auf den Keim schon äusserlich an diesen letzteren sichtbar sein kann. Darwin führt mehrere hierher gehörige Fälle an, und wahrscheinlich sind auch die Resultate der von Gärtner über diesen Gegenstand ausgeführten Experimente hier zu erwähnen, wenn es auch nicht ganz deutlich ist, ob der von Gärtner erwähnte directe Einfluss des Pollens sich nur innerhalb der Grenzen des Keimes merklich macht oder nicht.” p. 490.86Appendix to paper of Goss,Trans. Hort. Soc.v. 1822, pub. 1824 (not1848, as given by Professor Weldon), p. 236.87Since the above passage was written I find the “Imperials” described in “Report of Chiswick Trials,”Proc. R. Hort. Soc.1860,I.p. 340, as “skin thick”; and on p. 360 “skin thick, blue”; which finally disposes of this “exception.”88(36), p. 502 and (37), p. 663.89Professor Weldon should have alluded to this.Deadseeds have no bearing on these questions, seeing that their characters may be pathological. The same seeds are later described as “wie Telephone selbst,” so, apart from the possibility of death, they may also have been self-fertilised.90“Vielleicht sind einige der l.c. 507 bis 508 erwähnten fraglichen Fälle auf ähnliche vereinzelte Anomalien der Merkmalswerthigkeit zu beziehen; einige erwiesen sich allerdings beim Anbau als Producte ungewollter Selbstbefruchtung, andere keimten nicht.”91Regarding this case I have to thank Professor Correns for a good deal of information which he kindly sent me in response to my inquiry. I am thus able to supplement the published account in some particulars.92Mr Hurst, of Burbage, tells me that in varieties having coats green or white, e.g.American Wonder, the white coats are mostly from early, the green from later pods, the tints depending on conditions and exposure.93In the first caseKnight’s MarrowwithVictoria, both ways; in the secondVictoriawithTelephone, both ways.94Gärtner’smacrospermumwas evidently one of these, though from the further account (p. 498) it was probably more wrinkled. There are of coursemange-toutswhich have perfectly round seeds. Mendel himself showed that themange-toutcharacter, the soft constricted pod, was transferable. There are alsomange-toutswith fully wrinkled seeds and “grey” peas with small seeds (see Vilmorin-Andrieux,Plantes Potagères, 1883).95Correns found a similar result.96“Entweder kugelrund oder rundlich, die Einsenkungen, wenn welche an der Oberfläche vorkommen, immer nur seicht, oder sie sind unregelmässig kantig, tief runzlig(P. quadratum).”97The colour is the peculiarly deep yellow of the “grey”mange-tout.98It is certainly subject to considerable changes according to conditions. Those ripened in my garden are without exception much larger and flatter than Vilmorin’s seeds (now two years old) from which they grew. The colour of the coats is also much duller. These changes are just what is to be expected from the English climate—taken with the fact that my sample of this variety was late sown.99Thus avoiding the error of Seton, see p. 144. There is no xenia perhaps because the seed-coat of mother was a transparent coat.100As heterozygotes often do.101Dominance of the purple form.102Dominance of the grey coat as a maternal character.103Sherwood’s view (J. R. Hort. Soc.XXII.p. 252) that this was the origin of the “Wrinkled” pea, seems very dubious.104It will be well known to all practical horticulturalists that Laxton, originally of Stamford, made and brought out a large number of the best known modern peas. The firm is now in Bedford.105A round white ♀ × grey ♂ giving the usual result, round, “white” (yellow) seeds.106Tall heterozygotes, with normal dominance of purple flowers.107Here we see dominance of thepigmentedseed-coat as a maternal character overwhiteseed-coat. The colours of the seed-coats are described as essentially two: maple or brown-streaked, and violet, the latter being a small minority. As the sequel shows, the latter are heterozygotes, not breeding true. Now Mendel found, and the fact has been confirmed both by Correns and myself, that crossing a grey pea which is capable of producing purple leads to such production as a form of xenia.We have here therefore in the purple seeds the union of dissimilar gametes, with production of xenia. But as the brown-streaked seeds are also in part heterozygous, the splitting of a compound allelomorph has probably taken place, though without precise statistics and allotment of offspring among the several seeds the point is uncertain. The colour of seed-coats in “grey” peas and probably “maples” also is, as was stated on p. 150, sensitive to conditions, but the whole difference between “maples” and purple is too much to attribute safely to such irregularity. “Maple” is the word used to describe certain seed-coats which are pigmented with intricate brown mottlings on a paler buff ground. In French they areperdrix.108This is not, as it stands, explicable. It seems from this point and also from what follows that if the account is truly given, some of the plants may have been mosaic with segregation of characters in particular flowers; but see subsequent note.109As, commonly, in heterozygotes when fertile.110Recessive in flower-colour, seed-coat colour, and in seed-shape as a maternal character: pure recessives as the sequel proved.111These are then a mixture of pure dominants and cross-bred dominants, and are now inextricably confused. This time the round seeds may have been all on particular plants—showing recessive seed-shape as a maternal character. It seems just possible that this fact suggested the idea of “round” seeds on thecolouredplants in the last generation. Till that result is confirmed it should be regarded as very doubtful on the evidence. But we cannot at the present time be sure how much difference there was between these round seeds and thenormalmaples in point of shape; and on the whole it seems most probable that the roundness was a mere fluctuation, such as commonly occurs among the peas with large indented seeds.112Is this really evidence of segregation of characters, the flower being the unit? In any case the possibility makes the experiment well worth repeating, especially as Correns has seen a phenomenon conceivably similar.113Being a mixture of heterozygotes (probably involving several pairs of allelomorphs) and homozygotes.114This looks as if the violet colour was merely due to irregularity of xenia.115Pure recessives.116Pure recessives in coats showing maternal dominant character.117Now recognized as pure homozygotes.118This seems almost certainly segregation by flower-units, and is as yet inexplicable on any other hypothesis. Especially paradoxical is the presence of “white” seeds on these plants. The impression is scarcely resistible that some remarkable phenomenon of segregation was really seen here.119Being now homozygotes.120Being heterozygotes exclusively.121The nature of this mistake is now clear; for as stated above xenia is only likely to occur when the maternal seed-coat is pigmented. The violet coats in this experiment are themselves cases of xenia.122Knight, it was seen, crossed round ♀ × indented ♂ and consequently got no change of form.123Cotyledons seen through coat.124Ordinary dominance of round.125This is an extraordinary statement to be given as a general truth. There are sometimes indications of this kind, but certainly the facts are not usually as here stated.126If we were obliged to suppose that this is a matured conclusion based on detailed observation it would of course constitute the most serious “exception” yet recorded. But it is clear that the five statements are not mutually consistent. We have dominance of round white in first cross.In the second generation blue wrinkled give only blue wrinkled, and blue round give blue wrinkled and round, in accordance with general experience. But we are told that white round giveonlywhite round. This would be true of some white rounds, but not, according to general experience, of all. Lastly we are toldwhite wrinkled give all four classes. If we had not been just told by Laxton that the first cross showed dominance of white round, and that blue wrinkled and blue round give the Mendelian result, I should hesitate in face of this positive statement, but as it is inconsistent with the rest of the story I think it is unquestionably an error of statement. The context, and the argument based on the maple crosses show clearly also what was in Laxton’s mind. He plainly expected the characters of the original pure varieties to separate out according to their original combinations, and this expectation confused his memory and general impressions. This, at least, until any such result is got by a fresh observer, using strict methods, is the only acceptable account.Of the same nature is the statement given by the late Mr Masters to Darwin (Animals and Plants,I.p. 318) that blue round, white round, blue wrinkled, and white wrinkled, all reproduced all four sorts during successive years. Seeing that one sort would give all four, and two would give two kinds, without special counting such an impression might easily be produced. There are the further difficulties due to seed-coat colour, and the fact that the distinction between round and wrinkled may need some discrimination. The sorts are not named, and the case cannot be further tested.127See later.128The number in Haage and Schmidt’s list exceeds 200, counting colour-varieties.129The original passage is inLandwirths. Versuchstationen, 1888,XXXV.[notXXXIV.], p. 151.130“Es ist sogar sehr schwierig, einen Unterschied in der Farbe der Kreuzungsprodukte von Karmin und Weiss gegenüber Dunkelblau oder Violett und Weiss zu erkennen.”131See also the case ofBuchsbaum, p. 146, which received similar treatment.132One of the peculiarities of mostdouble“sulphur” races is that the singles they throw arewhite. See Vilmorin,Fleurs de pleine Terre, 1866, p. 354,note. InWien. Ill. Gartenztg.1891, p. 74, mention is made of a new race with singles also “sulphur,” cp.Gartenztg.1884, p. 46. Messrs Haage and Schmidt have kindly written to me that this new race has the alleged property, but that six other yellow races (two distinct colours) throw their singles white.133Biol. Cblt.XIV.1894, p. 79.134The various “contradictions” which Professor Weldon suggests exist between Crampe, von Guaita and Colladon can almost certainly be explained by this circumstance. For Professor Weldon “wild-coloured” mice, however produced, are “wild-coloured” mice and no more (see Introduction).135“Das Resultat einer Kreuzung zwischen Albino- und Normal-form ist stets, also, constant, ein dem Vater mindestens in der Färbung gleiches Junge.” This law is predicated for the case in which both parents belong to the same species.136“Dieses Alles ist abernieder Fall bei Kreuzungen unter Leucismen und normalen Thieren innerhalb der Species, bei denenstets und ohne jede Ausnahme die Jungen in Färbung dem Vater gleichen.”137He even withdraws two cases of his own previously published, in which grey and albino mice were alleged to have given mixtures, saying that this result must have been due to the broods having been accidentally mixed by the servants in his absence.138Excluding “false hybridisations.”139This is of course on account of the maternal seed characters. Unless the coat-characters are treated separately from the cotyledon-characters Laxton’s description is very accurate. Both this and the statements respecting the “shape” of the seeds, a term which as used by Laxton means much more than merely “wrinkled” and “smooth,” are recognizably true as general statements.140Separation of hypallelomorphs.141The combinations being exhausted. Perhaps Professor Weldon thought his authority was here lapsing into palpable nonsense!142Laxton constantly refers to this conception of the “climax” of—as we now perceive—analytical variation and recombination. Many citations could be given respecting his views on this “climax” (cp. p. 167).143Further subdivision and recombination of hypallelomorphs.144For instance thetallsproduced by crossingdwarfsare such “mules.” Tschermak found in certain cases distinct increase in height in such a case, though not always (p. 531).145“The remarkably fine but unfixable peaEvolution.” Laxton, p. 37.146Apart from fresh original variations, and perhaps in some cases imperfect homozygosis of some hypallelomorphs.147Mendel, on the contrary, disregards the “condition of the character” in the parent altogether; but is solely concerned with the nature of the characters of thegametes.148Regarding this “exception” see p. 146.149See p. 148.150Where was that “logician,” the “consulting-partner,” when this piece of reasoning passed the firm?151“Speichergewebe gelblich—oder weisslich—grün, manchmal auch vollständig hellgelb.” Tschermak (36), p. 480.152In his latest publication on this subject, the notes to the edition of Mendel in Ostwald’sKlassiker(pp. 60–61), Tschermak, who has seen more true exceptions than any other observer, thus refers to them. As to dominance:—“Immerhin kommen vereinzelt auch zweifellose Fälle von Merkmalmischung, d. h. Uebergangsformen zwischen gelber und grüner Farbe, runder und runzeliger Form vor, die sich in weiteren Generationen wie dominantmerkmalige Mischlinge verhalten.” As to purity of the extracted recessives:—Ganz vereinzelt scheinen Ausnahmsfälle vorzukommen."Küster (22) also in a recent note on Mendelism points out, with reason, that the number of “exceptions” to dominance that we shall find, depends simply on the stringency with which the supposed “law” is drawn. The same writer remarks further that Mendel makes no such rigid definition of dominance as his followers have done.153If the “logician-consulting-partner” will successfully apply thisFallacia acervalis, the “method of the vanishing heap,” to dominant peas, he will need considerable leisure.154I have no doubt there is no universal dominance in eye-colour. Is itquitecertain there is no dominance at all? I have searched the works of Galton and Pearson relating to this subject without finding a clear proof. If there is in them material for this decision may perhaps be pardoned for failing to discover it, since the tabulations are not prepared with this point in view. Reference to the original records would soon clear up the point.155See Wichura (46), pp. 55–6.156See above, p. 192.157See above, p. 187.158See above, p. 184.159See above, p. 186.160Beyond an indication as to the homogeneity or “purity” of its gametes at a given time.161May there be a connection between the extraordinary fertility and success of theTelephonegroup of peas, and the peculiar frequency of a blended or mosaic condition of their allelomorphs? The conjecture may be wild, but it is not impossible that the two phenomena may be interdependent.162This discussion leaves “false hybridism” for separate consideration.163Another practical point of the same nature arises from the great variability which these peas manifest in plant- as well as seed-characters. Mr Hurst of Burbage tells me that ine.g.William the First, a pea very variable in seed-characters also, tall plants may be so common that they have to be rogued out even when the variety is grown for the vegetable market, and that the same is true of several such varieties. It seems by no means improbable that it is by such roguing that the unstable mosaic or blend-form is preserved. In a thoroughly stable variety such asNe Plus Ultraroguing is hardly necessary even for the seed-market.Mr N. N. Sherwood in his useful account of the origin and races of peas (Jour. R. Hort. Soc.XXII.1899, p. 254) alludes to the great instability of this class of pea. To Laxton, he says, “we are indebted for a peculiar type of Pea, a round seed with a very slight indent, the first of this class sent out beingWilliam the First, the object being to get a very early blue-seeded indented Pea of the same earliness as the Sangster type with a blue seed, or in other words with a Wrinkled Pea flavour. This type of Pea is most difficult to keep true on account of the slight taint of the Wrinkled Pea in the breed, which causes it to run back to the Round variety.”164In dealing with cases of decomposition or resolution of compound characters this consideration is of highest importance.

1Biometrika,I., 1902, Pt.II.

2Biometrika,I.Pt.I.p. 5.

3The first half of this paper is reprinted with additions and modifications from theJournal of the Royal Horticultural Society, 1900, vol.XXV., parts 1 and 2. Written almost immediately after the rediscovery of Mendel, it will be seen to be already in some measure out of date, but it may thus serve to show the relation of the new conceptions to the old.

4See later. Galton gave a simple diagrammatic representation of his law inNature, 1898, vol.LVII.p. 293.

5These we now recognize as examples of Mendelian ‘dominance.’

6Comptes Rendus, March 26, 1900, andBer. d. Deutsch. Bot. Ges.xviii. 1900, p. 83.

7This conception of discontinuity is of course pre-Mendelian.

8‘Versuche üb. Pflanzenhybriden’ in theVerh. d. Naturf. Ver. Brünn, iv. 1865.

9Note that by these novel terms the complications involved by use of the expression “prepotent” are avoided.

10Professor Weldon (p. 232) takes great exception to this statement, which he considerately attributes to “some writers.” After examining the conclusions he obtained by algebraical study of Mendel’s figures I am disposed to think my statement not very far out.

11See later.

12Tschermak’s investigations were besides directed to a re-examination of the question of the absence of beneficial results on cross-fertilisingP. sativum, a subject already much investigated by Darwin, and upon this matter also important further evidence is given in great detail.

13For simplicity the case of self-fertilisation is omitted from this consideration.

14In all the cases discussed it is assumed that the gametes are similar except in regard to the “heritage” they bear, and that nooriginalvariation is taking place. The case of mosaics is also left wholly out of account (see later).

15The term “gamete” is now generally used as the equivalent of “germ-cell,” whether male or female, and the term “zygote” is here used for brevity to denote the organism resulting from fertilisation.

16In Pearson’s modification the parents contribute 0·3, the grandparents 0·15, the great-grandparents ·075.

17See the works referred to above.

18This conception was clearly formed by Naudin simultaneously with Mendel, but it was not worked out by him and remained a mere suggestion. In one place also Focke came very near to the same idea (see Bibliography).

19See von Guaita,Ber. naturf. Ges. FreiburgX. 1898 and XI. 1899, quoted by Professor Weldon (see later).

20This fact sufficiently indicates the difficulties involved in a superficial treatment of the phenomenon of reversion. To call such reversions as those named above “returns to ancestral type” would be, if more than a descriptive phrase were intended, quite misleading. It is not the ancestraltypethat has come back, but something else has come in its guise, as the offspring presently prove. For the first time we thus begin to get a rationale of “reversion.”

21It will be understood from what follows, that the existence of mosaic zygotes is noproofthat either component gamete was mosaic.

22A few additional particulars are given in Tschermak’s edition.

23[This translation was made by the Royal Horticultural Society, and is reprinted with modifications and corrections, by permission. The original paper was published in theVerh. naturf. Ver. in Brünn, Abhandlungen,IV.1865, which appeared in 1866.]

24[It is to the clear conception of these three primary necessities that the whole success of Mendel’s work is due. So far as I know this conception was absolutely new in his day.]

25[Mendel uses the terms “albumen” and “endosperm” somewhat loosely to denote the cotyledons, containing food-material, within the seed.]

26One species possesses a beautifully brownish-red coloured pod, which when ripening turns to violet and blue. Trials with this character were only begun last year. [Of these further experiments it seems no account was published. Correns has since worked with such a variety.]

27[This is often called the Mummy Pea. It shows slight fasciation. The form I know has white standard and salmon-red wings.]

28[In my account of these experiments (R.H.S. Journal, vol. xxv. p. 54) I misunderstood this paragraph and took “axis” to mean thefloralaxis, instead of the main axis of the plant. The unit of measurement, being indicated in the original by a dash (′), I carelessly took to have been aninch, but the translation here given is evidently correct.]

29[It is somewhat surprising that no mention is made of Thrips, which swarm in Pea flowers. I had come to the conclusion that this is a real source of error and I see Laxton held the same opinion.]

30[This also happens in Sweet Peas.]

31[Mendel throughout speaks of his cross-bred Peas as “hybrids,” a term which many restrict to the offspring of two distinctspecies. He, as he explains, held this to be only a question of degree.]

32[Note that Mendel, with true penetration, avoids speaking of the hybrid-character as “transmitted” by either parent, thus escaping the error pervading modern views of heredity.]

33[Gärtner, p. 223.]

34[It is much to be regretted that Mendel does not give the complete series individually. No one who repeats such experiments should fail to record theindividualnumbers, which on seriation are sure to be full of interest.]

35[This paragraph presents the view of the hybrid-character as something incidental to the hybrid, and not “transmitted” to it—a true and fundamental conception here expressed probably for the first time.]

36[This statement of Mendel’s in the light of present knowledge is open to some misconception. Though his work makes it evident that such varieties may exist, it is very unlikely that Mendel could have had seven pairs of varieties such that the members of each pair differed from each other inonlyone considerable character (wesentliches Merkmal). The point is probably of little theoretical or practical consequence, but a rather heavy stress is thrown on “wesentlich.”]

37[Note that Mendel does not state the cotyledon-colour of the first crosses in this case; for as the coats were thick, it could not have been seen without opening or peeling the seeds.]

38[“False hybridism” was of course unknown to Mendel.]

39[This and the preceding paragraph contain the essence of the Mendelian principles of heredity.]

40[To prove, namely, that both were similarly differentiated, and not one or other only.]

41[Whether segregation by such units is more than purely fortuitous could probably be determined by seriation.]

42[In the original the sign of equality (=) is here represented by +, evidently a misprint.]

43[This is the only passage where Mendel can be construed as asserting universal dominance forPisum; and even here, having regard to the rest of the paper, it is clearly unfair to represent him as predicating more than he had seen in his own experiments. Moreover in flower and seed-coat colour (which is here meant), using his characters dominance must be almost universal, if not quite.]

44[It appears to me clear that this expression is incorrectly given, and the argument regarding compound characters is consequently not legitimately developed. The original compound character should be represented asA1A2A3. . . which when fertilised bya1givesA1A2A3. . . a as the hybrid of the first generation. Mendel practically tells us these were all alike, and there is nothing to suggest that they were diverse. When on self-fertilisation, they break up, they will produce the gametes he specifies; but they may also produceA1A1andA2A2,A1A2a, &c., thereby introducing terms of a nature different from any indicated by him. That this point is one of the highest significance, both practical and theoretical, is evident at once.]

45[It seems very doubtful if the zygotes are correctly represented by the termsA1aA2a,A2aa,A1aa; for in the hybridsA1a, &c. the allelomorphsA1anda, &c. should by hypothesis be separated in the gametes.]

46InPisumit is placed beyond doubt that for the formation of the new embryo a perfect union of the elements of both fertilising cells must take place. How could we otherwise explain that among the offspring of the hybrids both original types reappear in equal numbers and with all their peculiarities? If the influence of the egg cell upon the pollen cell were only external, if it fulfilled therôleof a nurse only, then the result of each artificial fertilisation could be no other than that the developed hybrid should exactly resemble the pollen parent, or at any rate do so very closely. This the experiments so far have in no wise confirmed. An evident proof of the complete union of the contents of both cells is afforded by the experience gained on all sides that it is immaterial, as regards the form of the hybrid, which of the original species is the seed parent or which the pollen parent.

47“Welche in den Grundzellen derselben in lebendiger Wechselwirkung stehen.”

48“Dem einzelnen Beobachter kann leicht ein Differenziale entgehen.”

49[The argument of these two last paragraphs appears to be that though the general mutability of natural species might be doubtful, yet among cultivated plants the transference of characters may be accomplished, and may occur by integral steps until one species is definitely “transformed” into the other.]

50[Published inVerh. naturf. Ver. Brünn, Abhandlungen,VIII. 1869, p. 26, which appeared in 1870.]

51The plant used in this experiment is not exactly the typicalH. echioides. It appears to belong to the series transitional toH. præaltum, but approaches more nearly toH. echioidesand for this reason was reckoned as belonging to the latter.

52The words “general” and “universal” appear to be used by Professor Weldon as interchangeable. Cp. Weldon, p. 235 and elsewhere, with Abstract given below.

53These words occur p. 252: “The fundamental mistake which vitiates all work based upon Mendel’s method is the neglect of ancestry, and the attempt to regard the whole effect upon offspring produced by a particular parent, as due to the existence in the parent of particular structural characters, &c.” As a matter of fact the view indicated in these last words is especially repugnant to the Mendelian principle, as will be seen.

54I greatly regret that I have not a precise understanding of the basis of the modification proposed by Pearson. His treatment is in algebraical form and beyond me. Nevertheless I have every confidence that the arguments are good and the conclusion sound. I trust it may not be impossible for him to provide the non-mathematical reader with a paraphrase of his memoir. The arithmetical differences between the original and the modified law are of course clear.

55I have searched Professor Pearson’s paper in vain for any considerable reservation regarding or modification of this general statement. Professor Pearson enuntiates the law as “only correct on certain limiting hypotheses,” but he declares that of these the most important is “the absence of reproductive selection, i.e. the negligible correlation of fertility with the inherited character, and the absence of sexual selection.” The case of in-and-in breeding is also reserved.

56K. Pearson,Grammar of Science, 2nd ed. 1900, p. 36.

57Grammar of Science, 2nd ed. 1900, p. 480.

58Phil. Trans.1900, vol. 195, A, p. 121.

59“If this be done, we shall, I venture to think, keep not only our minds, but our points for observation, clearer; and further, the failure of Mr Galton’s statement in the one case will not in the least affect its validity in the other.” Pearson (32), p. 143.

60Grammar of Science, 1900, p. 494. See also Pearson,Proc. Roy. Soc.1900,LXVI.pp. 142–3.

61On an average of cases, in equal numbers, as Mendel found.

62Read in this connexion Pearson, K.,Grammar of Science, 2nd ed. 1900, pp. 390–2.Professor Weldon even now opens his essay with the statement—or perhaps reminiscence—that “it is perfectly possible and indeed probable that the difference between these forms of inheritance [blended, mosaic, and alternative] is only one of degree.” This may be true; but reasoning favourable to this proposition could equally be used to prove the difference between mechanical mixture and chemical combination to be a difference of degree.

62Read in this connexion Pearson, K.,Grammar of Science, 2nd ed. 1900, pp. 390–2.

Professor Weldon even now opens his essay with the statement—or perhaps reminiscence—that “it is perfectly possible and indeed probable that the difference between these forms of inheritance [blended, mosaic, and alternative] is only one of degree.” This may be true; but reasoning favourable to this proposition could equally be used to prove the difference between mechanical mixture and chemical combination to be a difference of degree.

63The whole question as to seed-coat colour is most complex. Conditions of growth and ripening have a great effect on it. Mr Arthur Sutton has shown me samples ofNe Plus Ultragrown in England and abroad. This pea has yellow cotyledons with seed-coats either yellow or “blue.” The foreign sample contained a much greater proportion of the former. He told me that generally speaking this is the case with samples ripened in a hot, dry climate.Unquestionable Xenia appears occasionally, and will be spoken of later. Moreover to experiment with such aplant-character an extra generation has to be sown and cultivated. Consequently the evidence is meagre.

Unquestionable Xenia appears occasionally, and will be spoken of later. Moreover to experiment with such aplant-character an extra generation has to be sown and cultivated. Consequently the evidence is meagre.

64Knowing my interest in this subject Professor Weldon was so good as to forward to me a series of his peas arranged to form a scale of colours and shapes, as represented in his Plate I. I have no doubt that the use of such colour-scales will much facilitate future study of these problems.

65I notice that Vilmorin in the well-knownPlantes Potagères, 1883, classifies the intermediate-coloured peas with thegreen.

66Similarly thoughtallanddwarfare Mendelian characters, peas occur of all heights and are usually classified as tall, half-dwarfs, and dwarfs.

67Wrinkling must of course be distinguished further from the squaring due to the peas pressing against each other in the pod.In connexion with these considerations I may mention that Vilmorin makes the interesting statement that most peas retain their vitality three years, dying as a rule rapidly after that time is passed, though occasionally seeds seven or eight years old are alive; but thatwrinkledpeas germinate as a rule less well than round, and do not retain their vitality so long as the round. Vilmorin-Andrieux,Plantes Potagères, 1883, p. 423. Similar statements regarding the behaviour of wrinkled peas in India are made by Firminger,Gardening for India, 3rd ed. 1874, p. 146.

67Wrinkling must of course be distinguished further from the squaring due to the peas pressing against each other in the pod.

In connexion with these considerations I may mention that Vilmorin makes the interesting statement that most peas retain their vitality three years, dying as a rule rapidly after that time is passed, though occasionally seeds seven or eight years old are alive; but thatwrinkledpeas germinate as a rule less well than round, and do not retain their vitality so long as the round. Vilmorin-Andrieux,Plantes Potagères, 1883, p. 423. Similar statements regarding the behaviour of wrinkled peas in India are made by Firminger,Gardening for India, 3rd ed. 1874, p. 146.

68Cotyledon-colour is not nearly so sensitive to ordinary changes in conditions as coat-colour, provided the coat be uninjured. But even in monomorphicgreenvarieties, a seed which for any cause has burst on ripening, has the exposed parts of its cotyledonsyellow. The same may be the case in seeds of green varieties injured byBruchusor birds. These facts make one hesitate before denying the effects of conditions on the cotyledon-colour even of uninjured seeds, and the variation described above may have been simply weathering. The seeds were gathered very late and many were burst inLaxton’s Alpha. I do not yet know they are alive.

69It is interesting to see that in at least one case the same—or practically the same—variety has been independently produced by different raisers, as we now perceive, by the fortuitous combination of similar allelomorphs.Sutton’s RingleaderandCarter’s First Crop(and two others) are cases in point, and it is peculiarly instructive to see that in the discussion of these varieties when they were new, one of the points indicating their identity was taken to be the fact that they producedthe same “rogues.”SeeGard. Chron.1865, pp. 482 and 603; 1866, p. 221; 1867, pp. 546 and 712.Rimpau quotes Blomeyer (Kultur der Landw. Nutzpflanzen, Leipzig, 1889, pp. 357 and 380) to the effect thatpurple-flowered plants withwrinkledseeds may spring as direct sports from peas withwhiteflowers androundseeds. I have not seen a copy of Blomeyer’s work. Probably this “wrinkling” was “indentation.”

Rimpau quotes Blomeyer (Kultur der Landw. Nutzpflanzen, Leipzig, 1889, pp. 357 and 380) to the effect thatpurple-flowered plants withwrinkledseeds may spring as direct sports from peas withwhiteflowers androundseeds. I have not seen a copy of Blomeyer’s work. Probably this “wrinkling” was “indentation.”

70The asymmetries here conceived may of course be combined in an inclusive symmetry. Till the differentiation can be optically recognized in the gametes we shall probably get no further with this part of the problem.

71Materials for the Study of Variation, 1894, p. 78.

72The varieties used wereExpress,Laxton’s Alpha,Fillbasket,McLean’s Blue Peter,Serpette nain blanc,British Queen,très nain de Bretagne, Sabre,mange-toutDebarbieux, and a large “grey” sugar-pea,pois sans parchemin géant à très large cosse. Not counting the last two, five are round and three are wrinkled. As to cotyledons, six have yellow and four have green. In about 80 crosses I saw no exception to dominance of yellow; but one apparently clear case of dominance of wrinkled and some doubtful ones.

73Professor Weldon may take this as a famous blow for Mendel, till he realizes what is meant by Mendel’s “Hybrid-character.”

74In addition to those spoken of later, where the great difference between reciprocals is due to thematernalcharacters of the seeds.

75I have not here considered the case in which male and female elements of a pure variety are not homologous and the variety is apermanentmonomorphic “mule.” Such a phenomenon, when present, will prove itself in reciprocal crossing. I know no such case in peas for certain.

76It will be understood that a “mule” form is quite distinct from what is generally described as a “blend.” One certain criterion of the “mule” form is the fact that it cannot be fixed, see p. 25. There is little doubt that Laxton had such a “mule” form when he speaks of “the remarkably fine but unfixable pea, Evolution.”J. R. Hort. Soc.XII.1890, p. 37 (v. infra).

77Using the word metaphorically.

78“Ueber die Blüthezeit der Hybriden sind die Versuche noch nicht abgeschlossen. So viel kann indessen schon angegeben werden, dass dieselbe fast genau in der Mitte zwischen jener der Samen- und Pollenpflanze steht, und die Entwicklung der Hybriden bezüglich dieses Merkmales wahrscheinlich in der nämlichen Weise erfolgt, wie es für die übrigen Merkmale der Fall ist.” Mendel, p. 23.

79As has been already shown the discovery could have been made equally well and possibly with greater rapidity in a case in which the hybrid had a character distinct from either parent. The cases that wouldnothave given a clear result are those where there is irregular dominance of one or other parent.

80Weldon, p. 240.

81See p. 43.

82In some transparent coats there is pigment, but so little as a rule that xenia would be scarcely noticeable.

83Usually correlated characters, as Mendel knew.

84Animals and Plants, 2nd ed. 1885, p. 428.

85“Eine andere Frage ist jedoch, ob der Einfluss des Pollens auf den Keim schon äusserlich an diesen letzteren sichtbar sein kann. Darwin führt mehrere hierher gehörige Fälle an, und wahrscheinlich sind auch die Resultate der von Gärtner über diesen Gegenstand ausgeführten Experimente hier zu erwähnen, wenn es auch nicht ganz deutlich ist, ob der von Gärtner erwähnte directe Einfluss des Pollens sich nur innerhalb der Grenzen des Keimes merklich macht oder nicht.” p. 490.

86Appendix to paper of Goss,Trans. Hort. Soc.v. 1822, pub. 1824 (not1848, as given by Professor Weldon), p. 236.

87Since the above passage was written I find the “Imperials” described in “Report of Chiswick Trials,”Proc. R. Hort. Soc.1860,I.p. 340, as “skin thick”; and on p. 360 “skin thick, blue”; which finally disposes of this “exception.”

88(36), p. 502 and (37), p. 663.

89Professor Weldon should have alluded to this.Deadseeds have no bearing on these questions, seeing that their characters may be pathological. The same seeds are later described as “wie Telephone selbst,” so, apart from the possibility of death, they may also have been self-fertilised.

90“Vielleicht sind einige der l.c. 507 bis 508 erwähnten fraglichen Fälle auf ähnliche vereinzelte Anomalien der Merkmalswerthigkeit zu beziehen; einige erwiesen sich allerdings beim Anbau als Producte ungewollter Selbstbefruchtung, andere keimten nicht.”

91Regarding this case I have to thank Professor Correns for a good deal of information which he kindly sent me in response to my inquiry. I am thus able to supplement the published account in some particulars.

92Mr Hurst, of Burbage, tells me that in varieties having coats green or white, e.g.American Wonder, the white coats are mostly from early, the green from later pods, the tints depending on conditions and exposure.

93In the first caseKnight’s MarrowwithVictoria, both ways; in the secondVictoriawithTelephone, both ways.

94Gärtner’smacrospermumwas evidently one of these, though from the further account (p. 498) it was probably more wrinkled. There are of coursemange-toutswhich have perfectly round seeds. Mendel himself showed that themange-toutcharacter, the soft constricted pod, was transferable. There are alsomange-toutswith fully wrinkled seeds and “grey” peas with small seeds (see Vilmorin-Andrieux,Plantes Potagères, 1883).

95Correns found a similar result.

96“Entweder kugelrund oder rundlich, die Einsenkungen, wenn welche an der Oberfläche vorkommen, immer nur seicht, oder sie sind unregelmässig kantig, tief runzlig(P. quadratum).”

97The colour is the peculiarly deep yellow of the “grey”mange-tout.

98It is certainly subject to considerable changes according to conditions. Those ripened in my garden are without exception much larger and flatter than Vilmorin’s seeds (now two years old) from which they grew. The colour of the coats is also much duller. These changes are just what is to be expected from the English climate—taken with the fact that my sample of this variety was late sown.

99Thus avoiding the error of Seton, see p. 144. There is no xenia perhaps because the seed-coat of mother was a transparent coat.

100As heterozygotes often do.

101Dominance of the purple form.

102Dominance of the grey coat as a maternal character.

103Sherwood’s view (J. R. Hort. Soc.XXII.p. 252) that this was the origin of the “Wrinkled” pea, seems very dubious.

104It will be well known to all practical horticulturalists that Laxton, originally of Stamford, made and brought out a large number of the best known modern peas. The firm is now in Bedford.

105A round white ♀ × grey ♂ giving the usual result, round, “white” (yellow) seeds.

106Tall heterozygotes, with normal dominance of purple flowers.

107Here we see dominance of thepigmentedseed-coat as a maternal character overwhiteseed-coat. The colours of the seed-coats are described as essentially two: maple or brown-streaked, and violet, the latter being a small minority. As the sequel shows, the latter are heterozygotes, not breeding true. Now Mendel found, and the fact has been confirmed both by Correns and myself, that crossing a grey pea which is capable of producing purple leads to such production as a form of xenia.We have here therefore in the purple seeds the union of dissimilar gametes, with production of xenia. But as the brown-streaked seeds are also in part heterozygous, the splitting of a compound allelomorph has probably taken place, though without precise statistics and allotment of offspring among the several seeds the point is uncertain. The colour of seed-coats in “grey” peas and probably “maples” also is, as was stated on p. 150, sensitive to conditions, but the whole difference between “maples” and purple is too much to attribute safely to such irregularity. “Maple” is the word used to describe certain seed-coats which are pigmented with intricate brown mottlings on a paler buff ground. In French they areperdrix.

We have here therefore in the purple seeds the union of dissimilar gametes, with production of xenia. But as the brown-streaked seeds are also in part heterozygous, the splitting of a compound allelomorph has probably taken place, though without precise statistics and allotment of offspring among the several seeds the point is uncertain. The colour of seed-coats in “grey” peas and probably “maples” also is, as was stated on p. 150, sensitive to conditions, but the whole difference between “maples” and purple is too much to attribute safely to such irregularity. “Maple” is the word used to describe certain seed-coats which are pigmented with intricate brown mottlings on a paler buff ground. In French they areperdrix.

108This is not, as it stands, explicable. It seems from this point and also from what follows that if the account is truly given, some of the plants may have been mosaic with segregation of characters in particular flowers; but see subsequent note.

109As, commonly, in heterozygotes when fertile.

110Recessive in flower-colour, seed-coat colour, and in seed-shape as a maternal character: pure recessives as the sequel proved.

111These are then a mixture of pure dominants and cross-bred dominants, and are now inextricably confused. This time the round seeds may have been all on particular plants—showing recessive seed-shape as a maternal character. It seems just possible that this fact suggested the idea of “round” seeds on thecolouredplants in the last generation. Till that result is confirmed it should be regarded as very doubtful on the evidence. But we cannot at the present time be sure how much difference there was between these round seeds and thenormalmaples in point of shape; and on the whole it seems most probable that the roundness was a mere fluctuation, such as commonly occurs among the peas with large indented seeds.

112Is this really evidence of segregation of characters, the flower being the unit? In any case the possibility makes the experiment well worth repeating, especially as Correns has seen a phenomenon conceivably similar.

113Being a mixture of heterozygotes (probably involving several pairs of allelomorphs) and homozygotes.

114This looks as if the violet colour was merely due to irregularity of xenia.

115Pure recessives.

116Pure recessives in coats showing maternal dominant character.

117Now recognized as pure homozygotes.

118This seems almost certainly segregation by flower-units, and is as yet inexplicable on any other hypothesis. Especially paradoxical is the presence of “white” seeds on these plants. The impression is scarcely resistible that some remarkable phenomenon of segregation was really seen here.

119Being now homozygotes.

120Being heterozygotes exclusively.

121The nature of this mistake is now clear; for as stated above xenia is only likely to occur when the maternal seed-coat is pigmented. The violet coats in this experiment are themselves cases of xenia.

122Knight, it was seen, crossed round ♀ × indented ♂ and consequently got no change of form.

123Cotyledons seen through coat.

124Ordinary dominance of round.

125This is an extraordinary statement to be given as a general truth. There are sometimes indications of this kind, but certainly the facts are not usually as here stated.

126If we were obliged to suppose that this is a matured conclusion based on detailed observation it would of course constitute the most serious “exception” yet recorded. But it is clear that the five statements are not mutually consistent. We have dominance of round white in first cross.In the second generation blue wrinkled give only blue wrinkled, and blue round give blue wrinkled and round, in accordance with general experience. But we are told that white round giveonlywhite round. This would be true of some white rounds, but not, according to general experience, of all. Lastly we are toldwhite wrinkled give all four classes. If we had not been just told by Laxton that the first cross showed dominance of white round, and that blue wrinkled and blue round give the Mendelian result, I should hesitate in face of this positive statement, but as it is inconsistent with the rest of the story I think it is unquestionably an error of statement. The context, and the argument based on the maple crosses show clearly also what was in Laxton’s mind. He plainly expected the characters of the original pure varieties to separate out according to their original combinations, and this expectation confused his memory and general impressions. This, at least, until any such result is got by a fresh observer, using strict methods, is the only acceptable account.Of the same nature is the statement given by the late Mr Masters to Darwin (Animals and Plants,I.p. 318) that blue round, white round, blue wrinkled, and white wrinkled, all reproduced all four sorts during successive years. Seeing that one sort would give all four, and two would give two kinds, without special counting such an impression might easily be produced. There are the further difficulties due to seed-coat colour, and the fact that the distinction between round and wrinkled may need some discrimination. The sorts are not named, and the case cannot be further tested.

In the second generation blue wrinkled give only blue wrinkled, and blue round give blue wrinkled and round, in accordance with general experience. But we are told that white round giveonlywhite round. This would be true of some white rounds, but not, according to general experience, of all. Lastly we are toldwhite wrinkled give all four classes. If we had not been just told by Laxton that the first cross showed dominance of white round, and that blue wrinkled and blue round give the Mendelian result, I should hesitate in face of this positive statement, but as it is inconsistent with the rest of the story I think it is unquestionably an error of statement. The context, and the argument based on the maple crosses show clearly also what was in Laxton’s mind. He plainly expected the characters of the original pure varieties to separate out according to their original combinations, and this expectation confused his memory and general impressions. This, at least, until any such result is got by a fresh observer, using strict methods, is the only acceptable account.

Of the same nature is the statement given by the late Mr Masters to Darwin (Animals and Plants,I.p. 318) that blue round, white round, blue wrinkled, and white wrinkled, all reproduced all four sorts during successive years. Seeing that one sort would give all four, and two would give two kinds, without special counting such an impression might easily be produced. There are the further difficulties due to seed-coat colour, and the fact that the distinction between round and wrinkled may need some discrimination. The sorts are not named, and the case cannot be further tested.

127See later.

128The number in Haage and Schmidt’s list exceeds 200, counting colour-varieties.

129The original passage is inLandwirths. Versuchstationen, 1888,XXXV.[notXXXIV.], p. 151.

130“Es ist sogar sehr schwierig, einen Unterschied in der Farbe der Kreuzungsprodukte von Karmin und Weiss gegenüber Dunkelblau oder Violett und Weiss zu erkennen.”

131See also the case ofBuchsbaum, p. 146, which received similar treatment.

132One of the peculiarities of mostdouble“sulphur” races is that the singles they throw arewhite. See Vilmorin,Fleurs de pleine Terre, 1866, p. 354,note. InWien. Ill. Gartenztg.1891, p. 74, mention is made of a new race with singles also “sulphur,” cp.Gartenztg.1884, p. 46. Messrs Haage and Schmidt have kindly written to me that this new race has the alleged property, but that six other yellow races (two distinct colours) throw their singles white.

133Biol. Cblt.XIV.1894, p. 79.

134The various “contradictions” which Professor Weldon suggests exist between Crampe, von Guaita and Colladon can almost certainly be explained by this circumstance. For Professor Weldon “wild-coloured” mice, however produced, are “wild-coloured” mice and no more (see Introduction).

135“Das Resultat einer Kreuzung zwischen Albino- und Normal-form ist stets, also, constant, ein dem Vater mindestens in der Färbung gleiches Junge.” This law is predicated for the case in which both parents belong to the same species.

136“Dieses Alles ist abernieder Fall bei Kreuzungen unter Leucismen und normalen Thieren innerhalb der Species, bei denenstets und ohne jede Ausnahme die Jungen in Färbung dem Vater gleichen.”

137He even withdraws two cases of his own previously published, in which grey and albino mice were alleged to have given mixtures, saying that this result must have been due to the broods having been accidentally mixed by the servants in his absence.

138Excluding “false hybridisations.”

139This is of course on account of the maternal seed characters. Unless the coat-characters are treated separately from the cotyledon-characters Laxton’s description is very accurate. Both this and the statements respecting the “shape” of the seeds, a term which as used by Laxton means much more than merely “wrinkled” and “smooth,” are recognizably true as general statements.

140Separation of hypallelomorphs.

141The combinations being exhausted. Perhaps Professor Weldon thought his authority was here lapsing into palpable nonsense!

142Laxton constantly refers to this conception of the “climax” of—as we now perceive—analytical variation and recombination. Many citations could be given respecting his views on this “climax” (cp. p. 167).

143Further subdivision and recombination of hypallelomorphs.

144For instance thetallsproduced by crossingdwarfsare such “mules.” Tschermak found in certain cases distinct increase in height in such a case, though not always (p. 531).

145“The remarkably fine but unfixable peaEvolution.” Laxton, p. 37.

146Apart from fresh original variations, and perhaps in some cases imperfect homozygosis of some hypallelomorphs.

147Mendel, on the contrary, disregards the “condition of the character” in the parent altogether; but is solely concerned with the nature of the characters of thegametes.

148Regarding this “exception” see p. 146.

149See p. 148.

150Where was that “logician,” the “consulting-partner,” when this piece of reasoning passed the firm?

151“Speichergewebe gelblich—oder weisslich—grün, manchmal auch vollständig hellgelb.” Tschermak (36), p. 480.

152In his latest publication on this subject, the notes to the edition of Mendel in Ostwald’sKlassiker(pp. 60–61), Tschermak, who has seen more true exceptions than any other observer, thus refers to them. As to dominance:—“Immerhin kommen vereinzelt auch zweifellose Fälle von Merkmalmischung, d. h. Uebergangsformen zwischen gelber und grüner Farbe, runder und runzeliger Form vor, die sich in weiteren Generationen wie dominantmerkmalige Mischlinge verhalten.” As to purity of the extracted recessives:—Ganz vereinzelt scheinen Ausnahmsfälle vorzukommen."Küster (22) also in a recent note on Mendelism points out, with reason, that the number of “exceptions” to dominance that we shall find, depends simply on the stringency with which the supposed “law” is drawn. The same writer remarks further that Mendel makes no such rigid definition of dominance as his followers have done.

Küster (22) also in a recent note on Mendelism points out, with reason, that the number of “exceptions” to dominance that we shall find, depends simply on the stringency with which the supposed “law” is drawn. The same writer remarks further that Mendel makes no such rigid definition of dominance as his followers have done.

153If the “logician-consulting-partner” will successfully apply thisFallacia acervalis, the “method of the vanishing heap,” to dominant peas, he will need considerable leisure.

154I have no doubt there is no universal dominance in eye-colour. Is itquitecertain there is no dominance at all? I have searched the works of Galton and Pearson relating to this subject without finding a clear proof. If there is in them material for this decision may perhaps be pardoned for failing to discover it, since the tabulations are not prepared with this point in view. Reference to the original records would soon clear up the point.

155See Wichura (46), pp. 55–6.

156See above, p. 192.

157See above, p. 187.

158See above, p. 184.

159See above, p. 186.

160Beyond an indication as to the homogeneity or “purity” of its gametes at a given time.

161May there be a connection between the extraordinary fertility and success of theTelephonegroup of peas, and the peculiar frequency of a blended or mosaic condition of their allelomorphs? The conjecture may be wild, but it is not impossible that the two phenomena may be interdependent.

162This discussion leaves “false hybridism” for separate consideration.

163Another practical point of the same nature arises from the great variability which these peas manifest in plant- as well as seed-characters. Mr Hurst of Burbage tells me that ine.g.William the First, a pea very variable in seed-characters also, tall plants may be so common that they have to be rogued out even when the variety is grown for the vegetable market, and that the same is true of several such varieties. It seems by no means improbable that it is by such roguing that the unstable mosaic or blend-form is preserved. In a thoroughly stable variety such asNe Plus Ultraroguing is hardly necessary even for the seed-market.Mr N. N. Sherwood in his useful account of the origin and races of peas (Jour. R. Hort. Soc.XXII.1899, p. 254) alludes to the great instability of this class of pea. To Laxton, he says, “we are indebted for a peculiar type of Pea, a round seed with a very slight indent, the first of this class sent out beingWilliam the First, the object being to get a very early blue-seeded indented Pea of the same earliness as the Sangster type with a blue seed, or in other words with a Wrinkled Pea flavour. This type of Pea is most difficult to keep true on account of the slight taint of the Wrinkled Pea in the breed, which causes it to run back to the Round variety.”

Mr N. N. Sherwood in his useful account of the origin and races of peas (Jour. R. Hort. Soc.XXII.1899, p. 254) alludes to the great instability of this class of pea. To Laxton, he says, “we are indebted for a peculiar type of Pea, a round seed with a very slight indent, the first of this class sent out beingWilliam the First, the object being to get a very early blue-seeded indented Pea of the same earliness as the Sangster type with a blue seed, or in other words with a Wrinkled Pea flavour. This type of Pea is most difficult to keep true on account of the slight taint of the Wrinkled Pea in the breed, which causes it to run back to the Round variety.”

164In dealing with cases of decomposition or resolution of compound characters this consideration is of highest importance.

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