An Amphidiploid I N the F 1 Generation from the Cross Oenothera Franciscanaxoenothera Biennis

ERTAIN peculiarities of the cross Oenothera franciscana Bartlett X OenoC them biennis L. led me to grow in recent years some large F1 families in one of which there appeared a tetraploid plant, the cytology and genetical behavior of which showed it to be an amphidiploid. This plant and its progeny will be the subject of this paper. The cross franciscanaxbiennis from parents out of long inbred lines produces in the F1 a progeny chiefly of light green, weak seedlings only a few of which live to develop small pale rosettes and these unable to live in the field. This was first recorded by DAVIS (1914, p. 189) and has been noted by later workers who have grown small families of the cross. But in contrast to the large progeny of light green, weak plants that die, there is a small group of dark green, strong seedlings which produce vigorous plants that come to flower in the field. The contrast between young rosettes of about the same age is shown in the text figure I; above are the parent types, franciscana a t the left and biennis a t the right; below are the two types of F1 hybrids. Combined data from three large cultures (35.71, 36.71, 36.77) with a germination of about 95 percent gave 3672 pale green seedlings and rosettes almost all of which died rapidly in pans and pots and none of which survived in the field or when given special attention in the greenhouse. There were 44 plants, dark green and strong, all of which matured, and among these were three triploids and the amphidiploid. The three triploids differed from the other plants of the dark green type in greater vigor, larger leaves, absence of red spots on the rosette leaves, and in green bud cones. Of the pollen scarcely IO percent of the grains seemed well developed, and these were probably infertile, since the plants produced no seed after numerous selfings, although forming large capsules when open pollinated. Cytological studies of meiosis in pollen mother cells of two plants showed that irregular distribution of the ZI chromosomes (10-1 I, 9-12, 8-13) characteristic of Oenothera triploids, and also showed frequent elimination of chromosomes through lagging on the spindle. The amphidiploid was distinguished markedly from the other dark green plants in the following respects: