Genetical studies on aenothera / Bradley moore Davis.

  • Davis, Bradley Moore.
Date:
1913
Catalogue details

Licence: In copyright

Credit: Genetical studies on aenothera / Bradley moore Davis. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    tain characters appears to advance as a whole presents the second problem to be considered. This phenomenon was also best exhibited by the F2 generations from the hybrids 10.30La and 10.30L5. A large number of plants in these cultures bore flowers with petals 1 cm. longer than those of the grandiflora parent (petals about 3.3 cm. long), and the smallest flowers were, for the most part, two or more times larger than those of the biennis pa- rent (petals about 1.3 cm. long); between these ex- tremes was a very perfect range of intermediates. An explanation for the advance in flower size over that of grandiflora may, of course, be offered as a recombina- tion of factors for large size on the hypothesis of mul- tiple factors for the size of petals, but why was there not a balancing group of plants with flowers as small as or smaller than those of biennis? Even the dwarfs of these cultures had flowers larger than those of the biennis pa- rent. The only plant having smaller petals was the ex- traordinary form 11.42; (Fig. 15). What had become in these cultures of the factors responsible for small size? A similar situation was presented by the character of the foliage most markedly exhibited by the F2 genera- tions from 10.30La and 11.35a. The leaves throughout the mass of these cultures were much larger than those of the parents of the cross and much more crinkled. There was thus a marked progressive advance in leaf size with the absence of small-leaved classes of plants unless such were represented in the F2 from 10.30La by the dwarfs. Admitting that possibility, the same prob- lem must be faced as was discussed for the explanation of the dwarfs themselves which were present in a ratio of about 1: 9, suggesting the 1:15 ratio with the presence of two factors for leaf size. Thus two factors for leaf size should give through the culture other classes besides those of the recessives, and these were not evident. Ap- plying the hypothesis of multiple factors for leaf size one is compelled to enquire what has become of the fac-