OF ENVIRONMENT 129 



When the root tips of the onion {Allium cepa) 

 were exposed for different periods of time to rays 

 from radium bromide of various degrees of activ- 

 ity, profound alterations were induced in the 

 mitoses of the cells. In nearly all cases the 

 passage of the chromosomes to the poles of the 

 spindle proceeded with great irregularity. Fre- 

 quently one or two chromosomes would remain 

 behind near the equator of the spindle, failing 

 completely to take part in the organization of the 

 daughter nuclei (Plate I, Fig. 6), At times 

 several chromosomes or portions of chromosomes 

 would remain at one side of the spindle, or be 

 carried beyond the poles (Fig. 8), or again be 

 drawn out as if subjected to considerable tension 

 (Fig. 5). In one instance, after the main cell- 

 division was nearly completed, a small secondary 

 spindle, in tardy telephase, was observed at one 

 side of the cell (Fig. 7) . 



From these results it was seen that the radium 

 treatment afforded a method by which chromatin 

 elements might be ehminated from reproductive 

 cells, and if these are the carriers of certain spe- 

 cific characters, as indicated by the researches of 

 Wilson, then a ready means of suppression or 

 substitution of characters would be afforded. In 

 addition to these distinctly radical effects, the 

 chromatin might be modified so as to form the 

 basis of characters not hitherto expressed by 

 the organism. 



Proceeding on this basis, Gager exposed to 



