362 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



The same writer exposed the ovules of plants to radium rays and pro- 

 duced marked changes in the germ cells so that they grew into various 

 stunted and otherwise abnormal plants, some of which bred true for 

 several generations. The work was not followed long enough to 

 determine whether the change was one involving a rather prolonged 

 induction or was a permanent mutation. ED.] 



FIG. 61. Two plants of Onagra bicnnis, showing the effect of injections of 

 zinc sulphate into the ovule. A, normal; B, the modified plant, which arose from 

 seeds that had been modified by zinc sulphate. (From MacDougal.) 



