644 Davis.—Cytological Studies on Oenothera. //. 
Cytological Discussion. 
The foregoing description of the reduction divisions in Oenothera 
biennis agrees with the account of Gates (’ 08 ) for O. rubrinervis , and Geerts 
(’ 09 ) for O. Lamar ckiana , in the following chief particulars :— 
1. The fourteen sporophytic (somatic) chromosomes that enter the 
heterotypic mitosis are formed by the segmenting of the spireme which 
follows synapsis, and are consequently arranged end to end. 
2. Although some of these fourteen chromosomes may be grouped in 
pairs at the equatorial plate of the heterotypic spindle, they are frequently 
so scattered as to be quite independent of one another. Under these con¬ 
ditions it seems impossible to distinguish two sets of chromosomes (such as 
might be regarded as of paternal and maternal origin), and there is possible 
a degree of irregularity in their distribution which is not generally present 
in the heterotypic mitosis, and was not present in the material of O. grandi- 
Jiora studied by the writer (Davis ’ 09 ). The heterotypic mitosis is a reduc¬ 
tion division. 
3. The chromosomes (after the lengthwise splitting in the anaphase of 
the heterotypic mitosis) may be followed through the interkinesis as seven 
pairs of chromosomes in each resting nucleus. 
4. The members of the seven pairs of chromosomes, present during 
the interkinesis, are distributed by the homotypic mitosis, which is therefore 
an equation division. 
The periods of the reduction divisions outlined above, that is from the 
segmentation of the spireme which follows synapsis to the conclusion of the 
homotypic mitosis, are the least difficult of all the phases to study. Never¬ 
theless this account of Oenothera biennis is not in agreement with the descrip¬ 
tions and figures of Gates and Geerts in a number of important particulars. 
The chief of these differences is in the structure of the chromosomes of the 
heterotypic mitosis, which in both biennis and grandijtora have the form of 
thickened V’s and are not subglobular as described and figured by Gates 
and Geerts. This divergence of results at a very characteristic stage of the 
reduction processes is but an example of a number of important differences 
between the writer’s accounts and those of the above authors at various 
phases of the periods under discussion. However, it does not seem best to 
discuss these different results in detail, since the reader can readily compare 
our various conclusions as shown by the figures. 
The phases of synapsis and presynapsis are very difficult of study, and 
there are better reasons to expect different accounts and interpretations on 
the part of investigators than in the stages following the appearance of the 
spireme as described in the above paragraph. Geerts gives very little 
information on the periods of synapsis and presynapsis in Oenothera 
Lamar ckiana. Gates (’ 08 , Fig. 17) figures for O. rubrinervis a close associa- 
