Cytological Studies on Oenothera. III. 
A Comparison of the Reduction Divisions of Oenothera 
Lamarckiana and O. gigas. 1 
BY 
BRADLEY MOORE DAVIS. 
With Plates LXXI-LXXIII. 
O F all the forms derived from Oenothera Lamarckiana which have 
appeared in the cultures of de Vries and others, O. gigas is to the 
writer by far the most interesting for the reason that we have in gigas 
a type sharply distinguished from Lamarckiana in a large number of 
particulars and clearly different in its nuclear structure, since it has twice the 
number of chromosomes present in the parent form. Whether others of the 
so-called mutants of Lamarckiana will show characteristic and stable differ¬ 
ences or peculiarities of the chromosomes or chromosome count becomes 
a matter of importance, and we are waiting with much interest for the 
results of investigations upon these forms. 
The writer (Davis, ’ll) has recently published an account of certain 
hybrids between Oenothera biennis and O. grandiflora that resemble 
Lamarckiana to such a degree as to justify, in his opinion, the consideration 
of a working hypothesis that Oenothera Lamarckiana arose as a hybrid 
between some strains of these two characteristic wild American species. The 
reasons, both experimental and historical, for this hypothesis will not be 
repeated here, especially since my studies in these directions are to be 
continued with other strains of these species that seem likely to give hybrids 
that will approach more closely to the desired end—the synthesis of a hybrid 
so similar to Lamarckiana as to be practically indistinguishable from this 
form by the usual taxonomic tests. 
Thus, although the bearing of the possible hybrid origin of Lamarckiana 
upon de Vries’ interpretation of the behaviour of this remarkable plant will 
not be discussed at this time, it will be apparent to the reader that if the 
evidence should finally indicate Lamarckiana to be of hybrid origin, as 
1 An investigation conducted with aid from the Elizabeth Thompson Science Fund, for which 
the author desires to express his indebtedness. 
[Annals of Botany, Vol. XXV. No. C. October, 1911.] 
3 Q 
