EFFECTS OF EXPOSING GERM-CELLS TO RAYS OF RADIUM 247 



characters, the effects being distributed unilaterally throughout the 

 plant as a whole because of the fact that the sporting occurred in the 

 terminal bud of the entire shoot-system. Even so, the initiation of 

 the sporting may be logically attributed to the radium rays, their 

 effects being brought into the offspring through the sperm-cell. But 

 thus we are brought back again to the idea of the plant as funda- 

 mentally and essentially a hybrid. 



Possible Induction of Mutation : The appearance in the 

 radium-cultures of elementary forms already recognized in normal 

 pedigreed cultures was rather to be expected, and the occurrence of 

 such a form is to be attributed to the influence of the rays only with 

 great caution. A description and discussion of a few aberrant forms 

 that appeared after the radium treatment follow. 



Among the progeny from an unexposed pistil whose stigma was 

 pollinated with pollen that had been exposed to rays from radium 

 bromide of 1,500,000 activity for 24 hours, there was found a seed- 

 ling with unusually narrow rosette leaves. Some of the characters 

 displayed by this plant at maturity are shown in the photograph, 

 PLATE 8. The narrowness of the rosette leaves is seen to have 

 persisted throughout the life of the plant. Furthermore its habit of 

 growth differs considerably from that of a mature biennis. In numer- 

 ous characters pertaining to the buds, petals, and mature capsules, it 

 differs from the biennis type. The specimen closely resembles an 

 elementary form observed by MacDougal ' in a normal pedigreed 

 culture, and described by him as a mutant. Other plants like this 

 one followed the treatment with the radium. 



The plant shown in plate 9 (5c of my cultures) is from seed 

 produced in an unexposed capsule with the stigma pollinated with 

 unexposed pollen, and then exposed to rays from radium bromide of 

 1,500,000 activity for 48 hours after pollination. It differs, not only 

 from the typical biennis, but also from the other variant forms ob- 

 tained. Following is a systematic description of the plant,* together 

 wilh the description of O. biennis as given in Britton and Brown's 

 "Illustrated Flora." 



* I wish to express here my best thanks to Dr. John K. Small, of the New York 

 Botanical Garden, for writing all of the sj'stematic descriptions in this chapter. They 

 were written without any knowledge on Dr. Small's part of the antecedent history of 

 the specimens. 



