426 BOTANICAL GAZETTE [DECEMBER 
O. Lamarckiana is about 2 per cent. Some of its mutations are 
themselves mutable and give 4 per cent or even 6 per cent of 
secondary mutations. The ordinary strains of O. pratincola 
produce about 2 per cent of mutations,‘ and the true O. biennis, of 
Holland, only about 0.45 per cent. In strains which show mass 
mutability, however, the number of mutations rises to 50 per cent 
or even 100 per cent. This is the case with Lexington E. 
Lexington E differs from all the other strains of O. pratincola 
(x) in that it gives rise to a characteristic group of four mutations, 
(2) in that these characteristic mutations occur in such large num- 
bers as to justify the use of the designation mass mutation for the 
phenomenon, and (3) in that it does not give rise to mut. num- 
mularia and certain other mutations which are characteristically 
produced by the strains which do not show mass mutation. 
Turning now to resemblances, we find absolutely no mor- 
phological characteristics to indicate even the slightest differ- 
ence between Lexington E and the other strains of O. pratincola. 
Moreover, Lexington E shows also the ordinary type of muta- 
bility, in that it gives rise to small numbers of some of the same 
mutations which the other strains produce. These mutations are 
in no wise distinguishable morphologically from the same forms 
occurring in the other strains, but all the evidence at hand shows 
that when derived from the strain showing mass mutation the 
non-characteristic mutations themselves show mass mutability. 
he mutations characteristic of mass mutability are themselves 
mutable and throw as secondary mutations other members of the 
characteristic group. 
In view of the extraordinary interest of the phenomenon of 
mass mutation, it is hoped that the reader will pardon the presenta- 
tion of this confessedly preliminary report. Many of the genetic 
relationships between the mutations and the parent species remain 
to be worked out, and, as will be very olga a cytological study 
of the whole subject is imperative. 
4 DeVries, H., Gruppenweise Artbildung. pp. 312-315. 
5 An estimate based upon the results tabulated in Bot. Gaz. 59:105-109. I915- 
VRIES, a The coefficient of mutability in Oenothera biennis L. Bor. Gaz. 
59:169~-196. I9 
