[46] In Pisum it 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 the rôle of 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 in Verh. naturf. Ver. Brünn, Abhandlungen, VIII. 1869, p. 26, which appeared in 1870.]
[51] The plant used in this experiment is not exactly the typical H. echioides. It appears to belong to the series transitional to H. præaltum, but approaches more nearly to H. echioides and for this reason was reckoned as belonging to the latter.
[52] The words “general” and “universal” appear to be used by Professor Weldon as interchangeable. Cp. Weldon, p. 235 and elsewhere, with Abstract given below.
[53] These 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.
[54] I 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.
[55] I 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.