Tricotyloiis Races Do Not Arise by Selection. 397 



shift the variabiHty in the half race in the plus direction 

 might perhaps be the same as those which would lead 

 to a mutation and thereby to the sudden origin of a 

 rich intermediate race. This would, in fact, perhaps, 

 constitute the smallest step amongst all the possible forms 

 of mutation.^ If a mutation were ultimately to be in- 

 duced by an improvement in the external conditions and 

 by the choice of individuals thus modified in the desired 

 direction,- it should most easily occur on the limits be- 

 tween the half race and the corresponding intermediate 

 race. My hope was, therefore, that an intermediate race 

 would suddenly arise from my improved half race and 

 at first give about 50%, and then, by further culture, 

 yield still higher numbers, perhaps even 80 to 90%. 

 This hope was based on the analogous case of the origin 

 of Chrysanthennun segetum plcmim from C. segctwn 

 grandiflorum ; for in this way tricotylous races behave 

 when they happen to be found and are isolated (see § 6). 

 A step of this kind I have, however, not yet observed. 

 In the case of both species I have determined the heredi- 

 tary capacity of as many as 300 seed-parents in a single 

 year, but without result. I have employed every device 

 of culture and in Scropludaria I sowed the seeds of the 

 second and sometimes those of the third year of the life 

 of the plant ; but every advance was followed by a step 

 in the reverse direction. I believe that I have tried everv- 

 thing that was possible to me at the time, and I liave 

 continued to make every conceival^le effort in spite of the 



* See p. 20 ; with regard to premutation. Vol. I, p. 490; and with 

 regard to varieties and subspecies, p. 64 of this vohime. 



^Alimentation ct selection. VoUunc jubilaire de la Societe de 

 Biologic, 1899; and Vol._ I, p. 142 of this work where the statement 

 is made that "selection is the choice of the best nourished individ- 

 uals." 



