1915] DE VRIES—OENOTHERA BIENNIS 179 
by actual crosses between different elementary types, such as we 
ordinarily suppose to occur in polymorphic groups in nature. 
The other alternative, that it is logically inconceivable that 
hybridism could have presided at the origin of new species, coin- 
cides exactly with the current conception of the mutability in the 
evening primroses. New forms originate through the evolution 
of new characters, as in O. gigas and O. rubricalyx;" or through 
the loss of existing ones, as in O. nanella and O. rubrinervis; or by 
means of the appearance of qualities, which were probably latent. 
in the parent race, as in O. lata and O. scintillans.* These cases 
are evidently not recombinations of existing characters. If it is 
conceded that the hypothesis of a hybrid origin does not apply to 
them, it is obviously unimportant for the theory whether or not, 
besides them, there are other instances which may be considered 
as hybrid recombinations. O. semigigas, which is a hybrid between 
a normal and a mutated sexual cell, has never been considered as 
an argument against the mutation theory. 
In cultures of chrysomelid beetles, W. L. Tower has observed 
hereditary changes which run almost parallel to the mutations of 
O. Lamarckiana. He started from crosses between Leptinotarsa 
decemlineaia, L. multitaeniata, and L. oblongata, and obtained 
constant races. When given proper treatment by changing their 
environic factors, these races could be made to break up, and they 
did so in a manner at least partially analogous to that of the 
evening primroses.” 
It is obvious that the fact that mutations may be artificially 
induced in hybrid strains does not contradict the contention that 
they may arise in pure strains also. But from the experiments of 
TOWER it seems that some by brid strains at least are more liable 
to show the phenomenon. 
7Q. gigas is considered to be a progressive mutant on account of its double number 
of chromosomes and its special behavior in crosses. O. rubricalyx, which arose in the 
: - x 
kindly supplied by him, is perhaps the most beautif mutants of 
Lamarckiana. Its s red color i is something quite | new in the group. i , Denaer asa 
gene pe isly of a pro- 
gressive nature; see Gates, R. R., ee Nat. 45:600. IgIt. 
*8 See Gruppenweise Artbildung. Berlin. pp. = 1913. 
* Tower, W. L., Evolution of the chrysomelid beetles. Carnegie Institution of 
Washington Yearbook no. 12:68-71. pl. 3. 1913- 
