236 EFFECTS OF EXPOSING GERM-CELLS TO RAYS OF RADIUM 



in mind it seems almost self-evident that such a natural group of 

 higher plants may not be artificially produced in the laboratory, nor, 

 indeed, within the narrow confines of an experimental garden. 



But whether we may artificially produce a parent or ancestor of 



Fig. 65. Onagra biennis. Permanently x\rrested Development. The Ovary, after 

 Pollination, was exposed for 53 Hours to the Rays from Radium Bromide (10,000 X) 

 Contained in a sealed Glass Tube. Cf. figure 66. 



a species is quite another question. A species has distinguishing 

 marks because the individuals that compose it have those marks, 

 and the group as a whole is separated from other groups of the same 

 systematic rank for at least two reasons : (i) Because its individual 

 members differ from the individual members of the other groups, 

 and (2) because these distinguishing characters, within the range of 



