Mendelism / by R.C. Punnett.

  • Punnett, Reginald Crundall, 1875-1967.
Date:
1912
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Mendelism / by R.C. Punnett. Source: Wellcome Collection.

    85/218 (page 59)
    VI REVERSION 59 cumbent plant with long internodes. This is the ordinary tall sweet-pea of the wild Sicilian type, reversion here, again, being due to the bringing together of two complementary factors which had somehow become separated in the course of evolution. To this interpretation it may be objected that the ordinary sweet-pea is a plant of upright habit. This, however, is not true. It only appears so because the conventional way of growing it is to train it up sticks. In reality it is of procumbent habit, with divergent stems like the ordinary Cupid, a fact which can easily be observed by any one who will watch them grow without the artificial aid of prepared supports. The cases of reversion with which we have so far dealt have been cases in which the reversion occurs as an immediate result of a cross, i.e. in the generation. This is perhaps the commonest mode of reversion, but instances are known in which the reversion that occurs when two pure types are crossed does not appear until the generation. Such a case we have already met with in the fowls' combs. It will be remembered that the cross between pure pea and pure rose gave walnut combs in F^, while in the F^ generation a definite proportion, i in i6, of single combs appeared (cf. p. 30). Now the single comb is the form that is found in the wild jungle fowl, which is generally regarded as the ancestor of the domestic breeds. If this is so, we have a case of reversion in F^ ; and this in the absence of the two factors brought together by the rose-comb and pea-comb parents. Instead of the reversion being due to the