No. 538] MUTATION IN (EN OTHER A 



not be doubted; but it is not clear that adaptation and 

 the larger evolutionary trends can be sufficiently ac- 

 counted for in this way, although occasional real germ- 

 inal advances are seen to occur. 



Summary 



It must be assumed that crossing has taken place in 

 the ancestry of CEnoihcra Lamarckiana, as well as in all 

 forms whose flowers are open-pollinated. Among open- 

 pollinated plants (and the same is probably true of ani- 

 mals) there is no such thing as a "pure" species, but 

 rather, many interbreeding races whose combinations 

 vary from generation to generation make up the popu- 



Further studies of historical records, and particularly 

 of early herbarium specimens, make it probable that the 

 "European biennis" so-called, rather than 0. Lamarcki- 

 ana, was the first Oenothera introduced into Europe. 

 Herbarium specimens show, however, that forms closely 

 resembling if not identical with 0. Lamarckiana and 0. 

 rubrinervis, formerly occurred wild in the western re- 

 gion of Colorado and New Mexico, and that other forms 

 which, from their flower characters, must be closely re- 

 lated to 0. Lamarckiana also occur there even now. 



Granting that 0. Lamarckiana must have undergone 

 crossing in its ancestry, it does not necessarily follow 

 that it has been synthesized by a single cross, such as 0. 

 grandiflora X 0. biennis. The fact that the characters 

 of the parents are usually blended in crosses between 

 Linmean species of (Enothera, while 0. Lamarckiana 

 agrees with 0. biennis in certain bud characters and with 

 0. grandiflora in certain other flower characters, does 

 not favor the hypothesis that 0. Lamarckiana originated 

 from this cross ; and the evidence offered by Davis is not 

 supported by a sufficiently critical study of the char- 

 acters of the three species concerned, the flowers of his 

 hybrids being little more than half the size of ordinary 

 6. Lamarckiana flowers. By selecting certain other 



