86 GENETICS [Bot. Absts., Vol. IV, 



561. Detjen, L. R. Some Fi hybrids of Vitis rotundifolia with related species and genera. 

 North Carolina Agric. Exp. Sta. Tech. Bull. 18:1-50. 33 fig. Aug., 1919.— Hybrid vines 

 derived from Vitis rotundifolia and species of Euvitis are usually more or less intermediate 

 in character. — The muscadine group when hybridized with species of Euvitis is not as pre- 

 potent in regard to its external visible characteristics as has generally been supposed. — 

 Hybrids derived from Vitis rotundifolia and species of Euvitis are almost sterile, due mainly 

 to hybridization. Perfect hermaphroditic forms are sterile from this cause alone, while im- 

 perfect hermaphroditic and staminate vines are sterile because of the double phenomenon of 

 sex or intersexualism and hybridization. — So-called "false hybrids" referred to in horticultural 

 literature as hybrids between Muscadine vines and species of Euvitis are not hybrids but 

 straight seedlings of the supposedly dominant parent species Vitis rotundifolia and Vitis 

 Munsoniana. — R-. A. Jehle. 



562. Detjen, L. R. The limits in hybridization of Vitis rotundifolia with related species 

 and genera. North Carolina Agric. Exp. Sta. Tech. Bull. 17: 1-25. July, 1919. — Vitis 

 rotundifolia will hybridize with V. Munsoniana and the following species of Euvitis; V. vini- 

 fcra, V. Bourquiniana, V. labrusca, V. cordifolia, and V. aestivalis, also with the varieties 

 Winchell, Concord, and others. — Vitis rotundifolia would not hybridize with Parthenocissus 

 tricuspidata, or Ampelopsis heterophylla var. elegans. — Vitis rotundifolia will hybridize 

 with its own Fi hybrids with other species of Vitis. — Vitis rotundifolia when used as a male 

 parent will hybridize quite readily with some species of Euvitis but when used as a female 

 parent it will hybridize only rarely. — R. A. Jehle. 



563. Detlefsen, J. A., and E. Roberts. Variation in the percentage of crossovers and 

 selection in Drosophila melanogaster. Anat. Rec. 17: 336. Jan. 20, 1920. [Author's abstract 

 of paper read before American Society of Zoologists, St. Louis, December 30, 1919.] — Series 

 A. Long-winged red-eyed F! females heterozygous in miniature wing and white eye were 

 mated in pairs to their miniature-winged white-eyed Fi brothers. The F2 offspring of the 

 Fi female showing the lowest percentage of crossing over were selected and mated. Con- 

 tinued inbreeding and selection gave a stock showing about per cent crossovers at the end 

 of ten generations, as compared with 33 per cent at the beginning of the experiment. This 

 stock bred en masse for 6 more generations continued to give about per cent crossovers. For 

 example, in the F15 we obtained 2 crossovers in a total of 977. — Series B. The same experiment 

 was begun a year later with stock entirely unrelated to that of series A. Inbreeding and 

 selection were continued for 28 generations and gave a stock showing 5 per cent crossovers, 

 as compared with the normal 33 per cent at the beginning of the experiment. The stock has 

 bred true to about 5 per cent crossovers for 10 generations. — Decrease in percentage of cross- 

 over has been accompanied by the increased appearance of non-disjunctional females. Tenta- 

 tively, we have concluded that selection has increased the amount of heterosynapsis which 

 would thus prevent the appearance of crossover classes. — J. A. Detlefsen and E. Roberts. 



564. Detlefsen, J. A., and E. Roberts. Linkage of genetic factors in mice. Anat. Rec. 

 17: 338. Jan. 20, 1920. [Author's abstract of paper read before American Society of Zoolo- 

 gists, St. Louis, December 30, 1919.] — Data were obtained to throw light on 17 of the possible 

 21 linkage relationships which may exist between any 2 of the following 7 allelomorphic 

 pairs: agouti vs. its absence, black vs. brown, dark eye vs. pink eye, self vs. recessive spotting, 

 dominant spotting vs. its absence, normal gait vs. waltzing, and color vs. albinism. In all 

 cases except those involving either black, or dark-eye, or self with normal gait, the hybrids 

 were mated back to the ultimate recessive to obtain data in the most advantageous form for 

 disclosing linkage. In the exceptional cases the Fi generation was mated inter se. As a 

 test against simple Mendelian recombination, sixteen of the seventeen cases showed no wide 

 deviations, and thus rule out any linkage except of such a loose nature that enormous num- 

 bers would be required to show it, which, for pracl ical purposes is tantamount to no linkage. 

 In the case of dark eye and color, a definite linkage was found, both when the Fi was mated 

 inter se and when back-crosses were made to the ultimate recessive. The latter case is the 



