CHAPTER XVIII 



EFFECTS OF EXPOSING GERM-CELLS TO THE RAYS OF 



RADIUM 



At the New York meeting of the American Association for the 

 Advancement of Science (1906-7), I announced^ before Section G 

 that certain results had been obtained by exposing egg- and sperm- 

 cells of Onagra biennis to radium rays, and that these effects were 

 character changes that gave promise, if inherited, of being of specific 

 value. That is, the results visible in ten-weeks old seedlings war- 

 ranted the expectation that the mature plants would differ from their 

 parent so profundly and fundamentally as to exclude their inclusion 

 within the species of the latter. Individual variation of certain char- 

 acters would fluctuate about a new mean. If these modifications 

 should prove to be transmitted in sexual reproduction, then the 

 new form would be entitled to at least the rank of the " elementary 

 species" of de Vries.* 



The species question, however, is here regarded as secondary to 

 that of variation. By whatever method or combination of methods 

 species are produced in nature, our immediate and fundamental 

 concern should be with the causes and behavior of variations. Varia- 

 tions are the materials out of which species are manufactured, and 

 it is essential in experimental work to center attention on the under- 

 lying question of variation before attempting to solve the problem of 

 how nature handles these variations in the making of a new species. 

 All this, in a sense, is a truism, but I state it here for the purpose of 

 making it clear that I do not believe that I have experimentally pro- 

 duced a new species. Nor indeed do I believe it probable that we 

 shall ever do so in the laboratory, at least with the higher green 

 plants. However much we may differ as to what a species is, the 

 term, as now used in taxonomy, always refers to a groiif of organ- 

 isms. The characters that distinguish the group as a grou^ are the 

 truly specific characters, and they develop under the influence of 

 forces that are not only physiological and ecological (in the strictest 

 sense), but also geographical and cosmical. With these facts clearly 



* Or, following Britton's* terminology, to the rank of a " race." 



235 



