208 Ferguson . — Development of the P o lien-tube and the 
and gives rise by segmentation to the chromosomes (Figs. 
30-33). Some of the ingrowing spindle-threads may extend 
across the nucleus to the nuclear membrane, which is still 
present on the upper side of the nucleus ; but by far the 
greater number unite some distance below this membrane 
to form several poles, thus giving rise to a diarch spindle 
(Strasburger, 1900 ), which is multipolar at its upper extremity, 
and unipolar, or nearly so, at its lower end. Gradually the 
poles of the upper portion draw together, while the spindle 
is somewhat shortened by the lower extremity of the threads 
being again resolved into granules. Finally a true bipolar 
diarch spindle is formed with the V-shaped chromosomes 
oriented at the nuclear plate. Each pole terminates in 
a slight granular condensation. The upper pole has never 
been observed to reach to the nuclear membrane, but 
frequently coarse granular threads extend from the pole to 
the wall of the nucleus, and apparently act as supports 
(Fig. 34). These are doubtless formed by a rearrangement 
of the linin reticulum. The nuclear membrane persists along 
the upper part of the nucleus until the late teleophase of the 
division (PI. XIII, Figs. 30-35, and PI. XIV, Fig. 38). 
As the chromosomes pass to the poles, the central spindle 
elongates so that the daughter-nuclei are separated, as a rule, 
by a greater distance than the original length of the spindle. 
While this is characteristic of cell-division in general, it is 
occasionally much exaggerated here, the daughter-nuclei 
being apparently forced apart with considerable energy. 
The nucleus which occupies the position nearest to the 
micropylar end of the ovule usually shows a deep indenta- 
tion along its upper surface as if a resistance had been met 
with in the peripheral layer of cytoplasm (Figs. 41 and 42). 
Not infrequently the upper nucleus is found almost entirely 
separated from the cytoplasm (Fig. 43). This, however, may 
be due to mechanical rupture during sectioning and staining. 
No cell-wall is ever formed, and in only one instance was 
a condensation of the spindle-threads in the region of the 
cell-plate observed (Fig. 40). The spindle may become 
