EFFECTS OF RADIUM RAYS ON PLANTS 1007 



self-pollinated. A necrotic area developed in the inflorescence where the 

 tube rested. The rate of flowering, size of the flowers, and "the fertility, 

 chiefly of the pollen," were affected more or less according to the dosage. 

 The percentage of germination was lowered for seeds in exposed capsules, 

 and morphological abnormalities appeared in the resulting seedlings. 

 Most of the atypical forms were too weak to survive field conditions. 

 One of the abnormal types, of Lamarckiana, when selfed, gave a progeny 

 in which the parent type composes approximately one-fourth (7 in 27) 

 of the population. When one of the abnormal plants from Oe. franciscana 

 was selfed, an entirely new form appeared, extremely weak and with 

 very linear mottled leaves. This form was not viable under field 

 conditions. 



In one of his early papers on mutation, de Vries noted that, if the 

 chromatin in reproductive cells could be altered by some external agent, 

 artificial mutation might be produced. He suggested that, by skillful 

 manipulation, this might be accomplished by bringing the sun's heat to a 

 focus on a nucleus by means of a burning glass. That experiment appears 

 never to have been successfully carried out, but the discovery of such 

 penetrating radiation as that given ofT by radium placed a convenient 

 device in the hands of experimental biologists. 



Koernicke (41) was perhaps the first botanist to perform this experi- 

 ment, using the pollen mother cells of Lilium Martagon. Within 20 hr. 

 after a 5-hr. exposure to radium rays the chromatin thread of the nuclei 

 of these cells was found to be broken up into double segments, much 

 smaller and more numerous than in normal, unexposed cells. Other 

 abnormalities were also figured, including the lagging behind and dropping 

 out of chromosomes during their passage to the daughter nuclei during 

 division. 



Experiments on cell-division in the root-tips of Allium cepa, reported 

 by Gager (25), included results similar to those of Koernicke. In some 

 cases, small masses of chromatin became stranded, so to speak, on one 

 side of the main nuclear spindle and organized a distinctly separate 

 spindle, resulting finally in two subsidiary daughter nuclei. In some 

 cases, the nuclei assumed amoeboid shapes, quite unlike anything seen 

 in normal, unexposed nuclei. 



The problem was investigated later by Opperman (60), who used 

 trout eggs fertilized with exposed sperms and reported results essentially 

 similar to those obtained by Gager and by Koernicke. These results 

 naturally suggested experiments for the purpose of ascertaining whether 

 true mutations may be produced by exposing germ cells to the action of 

 radium rays. 



At the meeting of the Deutsche Gesellschaft fiir Vererbungswissen- 

 schaft in August, 1921, Stein exhibited living plants, herbarium material, 

 and photographs to illustrate the effect of exposure to radium rays on 



