998 Gates.— Somatic Mitoses in Oenothera. 
chromosome in the nucleus of Fig. 9 shows such a split precociously. 
Fig. 10 represents the definitive shape of the chromosomes just before this 
split usually appears, and in Figs. 11 a and 11 h the fission is clearly visible 
in nearly every chromosome. At about this time the chromosomes also 
take up a more uniformly distributed peripheral position, and they may fre- 
quently have the appearance of an end-to-end arrangement, though they 
are not actually in contact, and their original arrangement was quite 
different. At the stage represented by Fig. 11 the chromosomes have also 
usually reached entire uniformity as regards size and shape. There are 
usually one to several nucleoli at this time, but occasionally, as in Fig. 10, 
no nucleolus is present. All the Figs. 1-11 are drawn from nuclei which 
were uncut by the knife. 
The first definite indications of lateral chromosome pairings appear at 
about the same time as the longitudinal split. Such a feature cannot be 
shown satisfactorily when the chromosomes are lying in three planes, but 
there are indications of such pairs in Fig. 11. 
The stage of the prophase in which the chromosomes are longitudinally 
split appears to last for some time. But it is soon followed by a stage 
(Fig. 12) in which the nuclear membrane has disappeared, the spindle has 
made its appearance as a delicate weft of fibrillae in the cytoplasm immedi- 
ately surrounding the nucleus, and the split in the chromosomes is no longer 
visible. The chromosomes are still grouped around the periphery of a 
sphere, as in the last stage, but the cavity of the nucleus has decreased 
somewhat, so that the chromosomes are more closely grouped, but they 
still partly retain the shape of curved rods, a shape assumed by the dia- 
kinetic chromosomes (Fig. 1 1) in accommodating themselves to the periphery 
of the nucleus. This stage is of short duration. Fig. 13 shows a later 
prophase, in which the spindle is beginning to assume a bipolar shape, and 
the chromosomes are being arranged on the equatorial plate. In this 
particular cell the chromosomes vary considerably from their usual shape, 
and the difference is not merely due to foreshortening. In studying large 
numbers of somatic mitoses, such variations in the shape of the chromo- 
somes are occasionally found. Their significance is not at present 
understood. 
Another case in which the shape of the chromosomes differed markedly 
from their normal shape in nucellar tissue is shown in Fig. 14. In this 
metaphase side view the chromosomes are short and thick, dumb-bell-shaped 
bodies, and they are also peculiarly distributed on the spindle, although the 
cell was undisturbed in cutting. All the chromosomes are not represented 
in the figure, and the full number could not be exactly determined. Fig. 15 
shows the position of this cell (b) in the ovule near the megaspore mother- 
cell (a), in which the heterotype mitosis is just completed, but no cell-wall 
has been formed. Such cases of variation in chromosome shape in particular 
