1918] DEVRIES—MASS MUTATIONS 421 
5. In other crosses of O. grandiflora the hybrids also resemble 
the corresponding ones of O. Lamarckiana. O. grandiflora X syrti- 
cola produces ‘the type gracilis, O. grandiflora Xbiennis hybrids of 
the types of biennis and ochracea, among which the first is constant 
in its progeny, whereas the second repeats the splitting. 
6. In crosses with O. Lamarckiana, O. grandiflora produces com- 
binations of the two groups of twins. I found three such types. 
One of them embraces about one-half of the offspring and corre- 
sponds to the /aeta; it is called ovata. The two others appear each 
in one-fourth of the whole culture and are called /utea and brunnea. 
The first corresponds to the combination ochracea Xvelutina, the 
second to grandiflora Xvelutina. These triple hybrids are constant 
in their progeny, inasmuch as they do not produce individuals of 
the other types, but split off some forms which constitute different 
combinations of the parental characters and partly also of those of 
the mutants. One of them, lacking the initial rosette of radical 
leaves, appears in percentage figures which seem to correspond to 
the formula of Mendel for monohybrids. 
7. If the crosses are made with the mutant Jorea, this character 
is latent in the first generation and reappears in the second in about 
one-quarter of the individuals; but this rule shows some exceptions. 
8. From these facts, in combination with the occurrence of about 
25 per cent of barren grains among the seeds, we arrived at the con- 
clusion that the yearly production of large numbers of ochracea is 
a phenomenon of mass mutation, analogous to the instances 
described by BARTLETT and due to an initial mutation of the ordi- 
nary rare type, followed by secondary mutation in the succeeding 
generations. 
9. This initial mutability of O. grandiflora must have yielded, 
besides the ordinary mutants, hybrid mutants, produced by the 
combination of a mutated sexual cell with a normal one. If then 
the offspring of this fecundation is assumed to split in a manner 
analogous to Mendel’s formula for monohybrids, three types must 
be the result. One of them is the mut. ochracea, which is now a 
secondary mutant; the second is the mutant hybrid of the type of 
the species, which will repeat the splitting; and the third must be 
a constant form of the same type. This last does not appear, and 
