July, 1922] 
CLELAND OENOTHERA FRANCISCANA 
409 
ogous chromosomes pair with entire regularity, and are carried to the 
equatorial plate and separated in a perfectly typical manner. In view 
of this suggestive study, it becomes of interest also to make a cytological 
study of Oe. franciscana, which is even more strikingly uniform in its 
behavior than Oe. grandiflora. The results of this study have been very 
interesting as indicating an even more striking regularity of chromosome 
behavior during the maturation divisions than that found in Oe. grandiflora. 
Not only do the chromosomes regularly pair with one another, but they 
show a most interesting uniformity of position, resulting in the linking 
of bivalent chromosomes in a seemingly constant manner; and, most 
striking of all, a definite morphological peculiarity, in the nature of a 
closed circle of four univalent chromosomes, is found to be always present 
during diakinesis, a feature which is most readily observable, and whose 
constancy is a clear reflection of the uniformity which characterizes the 
activity of the chromosomes as a whole at this time. 
It seems to be a fact, therefore, that the failure of homologous chromo- 
somes to pair at diakinesis, and the tendency for the chromosomes to 
come to the equatorial plate in an irregular fashion, are not characteristic 
of the genus Oenothera as a whole, but only of those species which have 
been found to be unstable. In the stable species, homologous chromo- 
somes seem to have a strong affinity for one another during diakinesis. 
In the unstable species, they seem to have little or no afhnity for one 
another, and the most obvious inference is that this incompatibility is 
due to the hybrid nature of the species. Such an inference may not be 
correct, however, as it may turn out, when a careful cytological and physio- 
logical investigation is made of pollen and ovule development in the more 
unstable species, that there is but one type of gamete present for each 
sex. If such be the case, then the irregularity of chromosome behavior is 
to be considered rather a morphological expression of the peculiar condi- 
tion, physiological or morphological, which results in the tendency to 
mutate. 
However this may be, the correlation between hereditary instability 
and the irregular behavior of chromosomes on the one hand, and between 
stability and the regular, uniform behavior of chromosomes on the other, 
is rather striking. Not only does it emphasize the probable purity of 
the stable species, but by contrast it should make one all the more cautious 
about considering the unstable ones as genetically pure. 
In conclusion, I wish to thank Dr. B. M. Davis for his great kindness 
in allowing me to make use of material growing in his gardens, in per- 
mitting me to include in this paper some of his unpublished data, as well 
as for the interest which he has manifested in the study as it has progressed. 
