108 BOTANICAL GAZETTE [FEBRUARY 
positions on the spindle. But they enter the daughter nuclei and 
divide again before the second spindle forms, and one of the 
products thus enters each spermatid. No such body is found in 
ovogenesis. 
The only previous suggestion of heterochromosomes in plants is in 
a.recent paper of CarpIFF (6), in which he mentions a heterotropic 
chromosome in the heterotypic mitoses of Salomonia biflora. He 
believes that this chromosome passes to one pole undivided in the 
first mitosis, but has not studied it further. 
The difference found in the number of chromosomes in the mutants 
of Oenothera very strongly favors considering these forms of “speci- 
fic” rank. I think it will be evident to any one studying carefully 
and comparing the different mutants that they are quite as distinct 
and easily distinguishable as are the species of any ordinary genus. 
The differences in the number of chromosomes is still further and, I 
think, conclusive evidence that the forms concerned are distinct 
“species.” i 
It seems necessary to conclude, therefore, that the phenomena 
of mutation as described by DeVries in the genus Oenothera are 
either due to O. Lamarckiana being some peculiar type of hybrid in 
which the earlier crosses are appearing again in comparatively rare 
numbers; or on the other hand that some process of differentiation, 
the most probable seat of which is the germ plasm, has led to the pro- 
duction of distinct types of germ cells differing in chromosome mor- 
phology and in hereditary value. The middle ground, the assump- 
tion that these various mutants are merely the widely fluctuating 
variations of the original O. Lamarckiana, is believed to be no 
longer tenable. 
Moreover, there are several lines of evidence, partly negative, 
which tend in various ways to discredit the possible hybrid origin of 
these forms. Some of these arguments will be mentioned. 
1. It has been clearly shown by MacDovucat (17, 18) and a 
number of collaborators that O. Lamarckiana was originally native 
to various parts of North America. 
2. If the mutants always existed together with the parent form, 
it seems probable that some at least would have been recognized as 
species and preserved in European or American herbaria. 
