2oS Heredity and Eiii^ciiics 



In Gager's experiments the action of radium ra}'S and 

 emanations upon plants are detinite, and in some instances 

 permanent modifications resulted (Fig. 72). In these 

 ex])eriments modilications b}" i)h)'sical and chemical agents 

 were produced which are not necessarily patliological, and 

 some of them continued to breed true in subsecjuent genera- 

 tions. 



Gager found that the action of radium raj-s upon jiollen 

 cells was to produce distortion of the karyokinetic figure 

 to the extent that chromosomes were left entirely out of 

 the spindle and were lost to that particular germ cell. 

 What happens in an}' particular variant whose modifica- 

 tions are inheritable has not been determined, but the sug- 

 gestion is at least plausible that the radium emanations in 

 some \\'a\' produce a new, or bring about a rearrangement 

 of the physiological complex which exists in the germ cell. 

 Conceivabl}- it may be due to the displacement of an indi- 

 vidual chromosome, although this suggestion would need 

 verification before it could be adopted. 



The modifications induced by the injections of salts 

 in MacDougal's experiments are not easy to understand. 

 The cells of the o\'ule are relatively impervious, and there 

 is a relatively small amount of dispersion from the scat of 

 the wound. The results obtained, however, are not due to 

 the effects of wounding, as shown by the fact that ovules 

 wounded in the same manner do not produce modifications 

 unless the salts are present; likewise, ovules stuiig bv insects 

 do not, as far as known, produce these results, and it is 

 only in ovules into which chemical salts have been injected 

 that modifications are effected. The conclusion seems un- 

 avoidable that the salts injected produced the observed 

 results bv modifving in some wav the constitution of the 



