Vol. 2 No. 7 



TORREYA LIBRARY 



T . NEW 



July, 19 o 2 



C 



THE ORIGIN OF SPECIES BY MUTATION* 



By D. T. MacDougal 



Admitting for the sake of the present discussion the validity of 

 the results obtained by de Vries, the following general laws may 

 be deduced from a consideration of the experimental observa- 

 tions recorded by him : 



i. New elementary species may originate suddenly, without 

 transition or intermediate forms between them and their imme- 

 diate ancestors. The new species actually originate in the forma- 

 tion of the seeds, but are born, figuratively speaking, at the time 

 of the germination of the seeds, and become recognizable in 

 many instances as soon as the earlier leaves have unfolded. 



2. The newly arisen species are constant from the moment of 

 their origin, and a species is not to ,be considered as an arbitrary 

 group but as consisting of a number of individuals conforming, 

 within the limits of the fluctuating variations, to a sharply defined 

 type. 



3. The new forms arising in the experimental investigations 

 were sufficiently divergent from the parents to be assigned spe- 

 cific rank, and might not be classed as varieties of the parent 

 types. 



4. The characters of the newly derived species show no re- 

 semblance to the individual variations exhibited by the parent 

 type, being in fact qualitative rather than quantitative divergences. 

 Special emphasis is to be laid upon this point, from which it would 

 seem that species do not appear by gradual differentiations 

 among plants growing wild in response to environmental stimuli, 



* Continued from page 84. 



[The exact date of publication of each issue of Torreya is given in the succeed- 

 ing number. Vol. 2, No. 6, comprising pages 81-96, was issued June 12, 1902.] 



97 



