1915] 
typica could be identified 
among them. The reciprocal 
cross yielded no seeds. 
Inheritance and mutability of 
the characteristic 
mutations 
Of the group of character- 
istic mutations, including mut. 
formosa, mut.. albicans, mut. 
revoluta, and mut. setacea, only 
the first is both normally fertile 
and vigorous. The second is 
vigorous, but produces few 
good seeds. The third is 
almost sterile, and the fourth 
is not only difficult to cultivate, 
but like mut. albicans gives 
very few good seeds. All of 
the forms were self-pollinated 
and reciprocally crossed with 
f. typica in 1914, but, except 
in the case of mut. formosa, 
the resulting F, cultures were 
very fragmentary or entire 
failures. The other three 
forms bloomed in September, 
when only a few weak, belated 
flowers of f. typica were avail- 
able for the crosses. The 
results of the cultures are 
summarized in table VI. 
Mut. formosa.—tThe 
entirely satisfactory cultures of 
this form show that it is con- 
stant in the sense that it gives 
no reversions to f. typica in its 
BARTLETT—MASS MUTATION 
progeny. 
445 
Fic. 9.—Mut. revoluta: a mature plant, 
Lexington E-19-21 (for position in pedigree 
see table IT) 
Moreover, there is no 
