Cell Structure, Growth and Division in the Antheridia of Polytrichum etc. 143 
A cluster of spindle fibers is attached at about the middle of each daughter 
chromosome (Figs. 49, 50) ; hence, as the latter is drawn toward the poles, its 
form approximates that of a U. It follows that two sister chromosomes are 
first separated from each other at the middle and remain in contact longest 
by their respective ends (Fig. 49). Sometimes (as in Fig. 51) a pair remain 
attached for some time by one end of each, becoming thus considerably 
stretched out as their middle parts are pulled poleward. Such an appearance 
has been rarely observed at an even later stage than that of Figure 51. 
After the chromosomes have reached the poles (PI. VII, Figs. 54 — 58 ; 
PI. VIII, Fig. 59), they become crowded together so closely that their indi- 
vidual outlines are difficult to distinguish. They are most distinctly 
seen at this time in polar view (see Fig. 56, PI. VII, from a cell at the same 
stage as that of Fig. 55). After reaching the poles, too, the chromosomes 
contract somewhat, becoming shorter and thicker (PI. VII, Figs. 57, 58 ; 
PI. VIII, Fig. 59). No nuclear membrane is discernible while the chromo- 
somes are massed together, although a relatively clear space appears 
on the side of each daughter group turned toward the equatorial plane 
(Fig. 59), due to a contraction of the central spindle fibers preparatory to 
cell plate formation. But as the chromosome group again becomes looser 
(Fig. 60), it is seen to be surrounded by a membrane, which encloses, besides 
the chromosomes, a gradually increasing amount of nuclear sap. The 
individual chromosomes are still unconnected. As the nucleus grows, 
the chromosomes become again longer and slenderer (Fig. 61) and ap- 
parently join end to end; at least, free ends are now rarely seen. 
The daughter nucleus passes gradually into the resting condition 
(Figs. 62 — 65). The daughter spirem loses its uniform thickness, and its 
Strands anastomose here and there; two or more nucleoles appear (Fig. 63). 
The arrangement of the newly-formed reticulum becomes more irregulär, 
and the nucleoles fuse into one (Fig. 64); this is at first rounded, but its 
outline, as a general thing, soon seems to become more angular (PI. VIII, 
Fig. 65 ; PI. VI, Fig. 1) and the nucleole larger, in all probability, as already 
suggested, through a massing about it of some of the chromatin. While 
these changes are occurring, the nucleus as a whole grows and changes 
from a lens-shaped to an approximately spherical body. The growth and 
rounding up of the nucleus do not, however, keep pace precisely with 
the other processes just mentioned; compare, for example, the large 
spherical daughter nuclei of Figure 64, Plate VIII, which retain much of the 
appearance of the dispirem stage, with the still much-flattened nuclei of 
Figure 62, whose chromatin seems to have gone much further toward the 
condition characteristic of the resting nucleus. 
