1915] BARTLETT—MASS MUTATION 453 
implicitly that he has made crosses only one way. If he had 
studied the reciprocals of his crosses it is safe to assume that he 
would never have ad- 
vanced his Mendelian 
explanation of muta- 
bility. As far as his 
results extend, his deriv- 
atives of O. Lamarcki- 
ana fall, for the most 
part, into two classes, 
which conform in heredi- 
tary behavior to the two 
main classes of muta- 
tions which have been 
obtained from O. pra- 
tincola. 
Class I.—The muta- 
tion breeds true, in the 
sense that it gives no 
reversions to the parent 
orm. The reciprocal 
crosses with the parent 
species are matroclinic. 
The progeny conforms 
to the type which sup- 
plies the female gamete. 
Class II.—The mu- 
tation gives a progeny 
consisting of the pa- 
rental and mutational 
types in greatly varying 
proportions. The pro- 
mutation supplies the 
Lex. 2S e358, AID 
oe MOGI = 
Fic —Mut. gigas (above) and f. typica (be- 
low): eae from the F, progeny of f. ty aged the 
-rosette of mut. gigas, Lexington E-5-238. had a 
darker color and more conspicuous pubescence than 
the sister plant of f. typica, but the difference does 
not appear in the photograph; both plants are 
sue in fig. 5 
female gametes, but consist of the parental type only if the muta- 
tion supplies the male gamete. 
