sex cells of rustica var. pumila and Bigelovii var. Wallacei were grown last summer. There was no evidence of variation in the latter and no appreciable reduction in fertility. In the case of rustica there were both dwarfs and plants of normal size, but little decrease in fertility in the former. The treatment was apparently gametically or zygotically lethal for suaveolens and almost so in the case of nudicaulis. The former produced non-viable seeds only, and from seed of the latter species only two plants grew to maturity. One of them was normal in appearance and in flower, while the other was decidedly dwarf and set no seed until late in the season and then only in cleistogamous flowers. It would seem probable that progenies from both variant and "normal" plants of the two X-rayings of tabacum will exhibit recessive modifications, as may progenies from the other species which received similar treatment. It is proposed as soon as possible to study the effects of variations in X-ray dosage on the nature of the heritable variations which we now know can be obtained, and possibly to determine comparative effects of X-ray treatment of seeds of species in which variation has already been produced by treatment of sex cells. A complete account of the cytology and genetics of the X-ray variants will appear in the Botanical Gazette. * A tall, large-leaved, red-flowered variety of the species of commerce, grown in the pure line for many years and extensively studied here in inter-and intraspecific hybrids (cf. Univ. Calif. Publ. Botany, vols. 5 and 11, and elsewhere).Crossing-Over.-The frequency of crossing-over in the C-Sh-Wx region in maize, though varying rather widely in different plants, is remarkably constant within the individual. Repeated pollinations from the same heterozygous plant throughout the pollen-shedding period show no significant variation in cross-over percentage, indicating (for the male germ cells) that considerable differences in age and wide fluctuation in temperature and other weather conditions have no appreciable effect on crossingover in this region.2 The discovery by Mavor3 that cross-over frequency in Drosophila is affected by X-rays even in the sex chromosome (in which Plough4 and Bridges5 had found crossing-over unaffected by age and temperature differences) suggested that cross-over variations in the C-Sh-Wx region might be induced by X-ray treatment. Later experiments by Muller6 indicated that certain regions in Drosophila are relatively immune to the effects of X-rays on crossing-over.
Changes were observed from miniature-alpha to beta and gamma, from niniature-beta to gamma, and from miniature-gamma to alpha and beta.Miniature-alpha appears to be the most unstable and miniature-beta the most stable of the three mutable miniature allelomorphs as far as the changes from one miniature allelomorph to another are concerned.l Demerec, M., these PROCUEDINGS, 12, 1926 (687-690).2 Miniature-l is constant allelomorph of mutable miniature and it is independent in origin of mutable miniature. It was found by Dr.In common barley (Hordeum vulgare) mutation is readily induced by X-rays.2 Hundreds of recessive mutations have occurred in this species under known conditions of treatment. The rate of mutation is proportional to radiation intensity, and under heavy dosage of dormant seed mutations have occurred at rates exceeding 5 per cent.The same treatments applied to common oats yield little or no induced mutation. In 1928 oats were included with barley in a number of experiments in which x-ray treatments were applied to dormant or germinating seeds. Oats of both of the commonly cultivated species, Avena saliva and A. byzantina, were included, the former species being represented by a selection of the agronomic variety Kherson and the latter by a selection of the variety Fulghum. The rate of mutation was determined for seedling characters only, previous trials having shown that about 90 per cent of the induced mutations were recognizable in the seedling stage. Only one mutation was found in the treated oats, a recessive white seedling segregating in the progeny of Kherson oats irradiated as dormant seed. The same treatments if applied to barley would have produced more than 40 mutations. This extreme difference in mutation rate between oats and barley is not surprising in view of the known chromosomal constitution of the species concerned. Following the discovery by Sakamura3 of a polyploid series in Triticum species, similar series have been found in Avena (Kihara4) and Hordeum (Griffee5). In each genus species with 7, 14 and 21 pairs of chromosomes occur. In Triticum and Avena the most valuable cul- 876 PROc, N. A. S.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.