138 THE DIRECT INFLUENCE 



are found among or between organs in a manner 

 difficult of explanation upon any ground except 

 that of simultaneous somatogenic induction. 



MECHANISM OF THE INHERITED CHANGE 



The modification of heredity brought about by 

 the direct action of various agencies upon the 

 germ-plasm is now safely established, and the 

 available results are sufficient to justify some few 

 generalizations as to the mechanism of the 

 change. The most important evidence as to the 

 nature of the disturbances which may ensue in 

 reproductive elements comes from the work of 

 Gager, who found that the action of radium 

 might eliminate definite chromatin elements dur- 

 ing the mitoses of the egg and pollen, and, fur- 

 thermore, that some of the eggs fertilized by 

 pollen subjected to such irradiation produced a 

 progeny in which qualities different from those of 

 the parental strain were exhibited. It is not 

 proven, of course, that the atypic strain was de- 

 rived from a fertilization into which one less or 

 one more chromosome entered, and possible dis- 

 turbances of the autolytic action of the cell might 

 well be as important as the departures from nor- 

 mal mitotic procedure. The well-known influ- 

 ence of temperatures upon these processes and 

 also the readiness with which unusual substances 

 might be thrown into the cytoplasm in the ordi- 

 nary course of nutrition, suggests that the plant 



