Pollen Mother-cells of Lilium canodense . 
215 
The Separation of the Daughter Chromosomes. 
My observations as to the orientation of the chromosomes in the 
equatorial plate, and their behaviour in the metaphases and anaphases, agree 
essentially with recent descriptions of Strasburger (’ 00 ) and Mottier (’ 03 ). 
In case of the attachment of the spindle fibres to one end of each 
daughter chromosome, the separation is completed by the untwisting of 
the daughter chromosomes, if any twist remains, and their gradual pulling 
apart, the separation beginning, of course, at the end to which the fibres 
are attached, and progressing toward the other end. The last points of 
contact between the daughter chromosomes are, therefore, at the end of 
each which was originally unattached to the spindle, in the case of the 
radial chromosomes at the outer end, this final contact occurring in the 
equatorial plane. Figs. 68 and 69 show the progress of this separation, 
as seen when looking at the spindle in the equatorial plane. These figures 
represent the chromosome viewed in the same way as in Fig. 64, but at 
later stages. The relative position of the outer ends of the daughter 
chromosomes, it is seen, changes with the degree of untwisting ; in Fig. 69, 
the end of one daughter chromosome is turned outward, that of the other 
toward the interior of the spindle. 
Figs. 70-72 show similar stages, the chromosomes being viewed 
laterally. Figs. 70 and 71 show about the same amount of twisting of 
the daughter chromosomes as appears in Figs. 60 and 63 ; Fig. 72, in 
which there is no twisting, is comparable with Fig. 61. Fig. 72 illustrates 
the often-observed phenomenon of an elongation or stretching of the 
separating portions of the daughter chromosomes, due to their plasticity. 
This plasticity of the chromosome material is also frequently shown by the 
appearance of a projection (Fig. 70) at the point to which the spindle 
fibres are attached ; the remaining substance of the attached end of the 
chromosome lags behind, as it were, giving to the daughter chromosome 
a slightly hooked form (Fig. 70), which is retained in the anaphases. From 
the more common radial arrangement of the chromosomes in the equatorial 
plate, and the attachment of the spindle fibres to the inner end of the 
daughter chromosomes on the side toward the pole, it is plain that this 
short hook will in most cases be turned toward the interior of the spindle, 
and so will not ordinarily be visible if the chromosome be viewed from the 
side turned outward ; either a lateral view, or one of that side of the 
chromosome turned toward the interior of the spindle, will be necessary 
to show the presence of the hook. 
At about the stage represented by Fig. 69, namely, that at which the 
daughter chromosomes remain in contact only by their equatorial ends, 
a longitudinal split (Figs. 58, 74-77) appears in each daughter chromosome. 
The occurrence of this split seems to be very sudden, and when first seen 
