REPORTS ON RESEARCH FOR 1926 
Genetics and Plant Breeding 
Influence of Radium Rays upon Hereditary Variations in the 
Jimson Weed, Datura Stramonium 
By C. Stuart GAGER 
In cooperation with 
A. F. BLAKESLEE, 
Department of Genetics, Carnegie Institution of Washington 
The Jimson Weed (Datura Stramoniunt) has shown itself es- 
pecially adapted to experimentation regarding the laws of in- 
heritance and evolution. Hereditary variation can be brought 
about either by mutative changes in the number of the hereditary 
bodies (chromosomes) or by mutations in the factors which 
these chromosomes contain. The discovery of any stimulus 
which will accelerate these processes of mutation, which are ex- 
tremely rare, would be of much scientific interest and might have | 
considerable economic importance, 
In continuation of the senior author’s earlier investigations on 
the effects of radium on plant tissues, he made a preliminary 
study of the effects of radium treatment upon the hereditary 
units in flowers of Jimson Weeds. From one of the three 
treated flowers there were obtained in the offspring: (a) 17.7 per 
cent. of chromosomal mutations, a much higher percentage 
than ever obtained from untreated capsules, the average for over 
15,000 offspring being 0.47 per cent., (b) a new compound chro- 
mosomal type, called Nubbin (from the character of the fruit- 
pod), in which some of the chromosomes appear to have been 
broken in two and joined together again in new combinations, (c) 
two new factor mutations out of 18 of the offspring tested. It 
is believed that the increase of chromosomal mutations was due 
to the radium treatment and that the radium may also have been 
responsible for the production of the compound chromosomai 
type Nubbin and for the two new factor mutations. Further 
experiments, however, will be necessary to determine whether in 
