1918] DEVRIES—MASS MUTATIONS 419 
normal gametes in the first species. If we assume this to be the 
true interpretation, the pedigree may be written in this form: 
O. grandiflora X biennis, or 
O. grandiflora typica X biennis +O. grandiflora ochracea X biennis 
| 
First generation— _ biennis ochracea 
Second generation— biennis ochracea — ochracea biennis 
Read in this way our experiments show that in the normal 
gametes of O. grandiflora the characters of the species are recessive 
to those of O. biennis, and that uniform and constant hybrids are 
produced. The gametes which repeated the mutation into 
ochracea, on the other hand, possessed dominant characters, and the 
offspring was hardly distinguishable from normal ochracea. But 
after self-fertilization it split off the biennis type, especially the 
character of producing stout initial rosettes before making a stem, 
and this splitting seems to conform to ‘Mendel’s law for mono- 
hybrids. 
H. ANALOGY BETWEEN THE TWINS OF 0. GRANDIFLORA AND 
LAMARCKIANA 
In concluding this article I might point out the striking analogy 
between the splitting phenomena of O. grandiflora and those of 
O. Lamarckiana. Evidently they must be considered as the results 
of the same internal causes. The chief difference is the absence of 
a visible mass mutation in the latter species. On the contrary, the 
amount of barren grains among its seeds is double that of O. grandi- 
flora. We are therefore induced to assume a second lethal factor, 
linked with the characters of ochracea and Jaeta, respectively, and 
killing the /aeta germs of O. Lamarckiana. Or, stating it in other 
words, we may imagine the factor for weakness, which causes the 
death of a large part of the ochracea mutants after germination, to 
be replaced in O. Lamarckiana by a lethal factor, which kills the 
corresponding germs before germination. 
RENNER (12) has proposed an explanation which in some 
respects parallels the views developed in this article, but, as I have 
