82 BOTANICAL GAZETTE [FEBRUARY 
and (3) that its habit of throwing off marked germinal variations 
is paralleled by the behavior of certain interspecific hybrids in the 
F, and F, generations seem to Davis' a sufficient indication that 
this plant is of comparatively recent hybrid origin, and that its 
mutations are due to germinal instability resulting from hybridiza- 
tion. He holds that the germinal variations of O. Lamarckiana 
and of various hybrids which he has studied show marked pro- | 
gressive evolution which seemingly cannot be accounted for on a 
Mendelian basis. Although he does not deny that slight discon- 
tinuous variations may occur in homozygous strains (and he insists 
that the term mutation ought to be used only for such variations), 
he is of the opinion that variations large enough to be of evolu- 
tionary significance occur rarely if at all except in heterozygous lines. 
Gates! does not believe that O. Lamarckiana is a recent inter- 
specific hybrid, but does ascribe its mutations to germinal insta- 
bility caused by occasional random crossing with other types. In 
their main conclusion, that when germinal variation occurs it 
usually follows crossing, Davis and GATEs appear to agree. GATES, 
however, is more emphatic than Davis in his conclusion that muta- 
tion in Oenothera is not merely a result of Mendelian redistribution 
of unit characters, but is a distinct type of variation. He believes, 
moreover, that mutation sometimes takes place in pure as well as 
in hybrid lines. Since the phenomena are identical in the two cases, 
he has laid especial stress on the fact that there is no excuse for 
confusing mutation, when it occurs in hybrids, with any type of 
Mendelian segregation.s 
Avis, B. M., Genetical studies on Oenothera. II. Amer. Nat. 45:193-233- 
ro11; Ill. Jbid. 46:377-427. 1912; IV. Ibid. 47:440-476, 547-571. feiss 
4Gates, R. R., Mutation in Oenothera. Amer. Nat. 45:577-606. 
conbrbetion to a pees of the mutating Paneer “Trans. 
Linn. Soc. pe II. Bot. 8:1-67. 
, Tetraploid mutants one sf mechanisms. Biol. Centralbl. 
33:92-99, 113-150. 1913. 
5In this author’s last paper he says: “The cytological evidence shows that 
germinal changes may and do occur which are independent of all the laws of hybrid 
combination and hybrid splitting. This cadenstiea ten | is of more fundamental signifi- 
cance than might at first appear; for it shows that mutation in Oenothera is a process 
sui generis, and that no amount of hybrid combination and splitting, Mendelian or 
otherwise, is sufficient to account for it.” Gates, R. R., Breeding experiments which 
show that hybridization and mutation are pees phenomena. Zeitschr. Ind. 
Abstammungs- u. Vererbungslehre 11: 209-279. 
