Pollen Mother-cells of Certain Plants . 
37 
each chromosome of the daughter nuclei may be followed as an individual 
entity, but I have not been able to follow the origin of the generic structure 
during the reconstruction stages. Each chromosome undergoes very little 
change, except to become slightly elongated and somewhat thinner (Fig. 25, 
PI. III). At this stage the nuclear membrane is present. The chromo- 
somes appear to be irregularly distributed in the nuclear cavity. One may 
often find chromosomes so closely associated as to appear united at their 
ends, while others lie apparently free in the nuclear cavity (Figs. 25 and 
26, PL III). Ultimately, however, all the chromosomes are arranged into 
a spirem, which is not entirely chromatic, but consists of chromosomes and 
linin intervals, just as I have described for the prophases of the first division. 
Each chromosome may have its chromatic portion somewhat distributed, 
but it is always seen to consist of its two daughter segments arranged side 
by side in this spirem. These daughter segments never separate or open 
apart as has been described for Lilium . In this stage the chromatin material 
appears somewhat reticulated (Figs. 2 6, 27, and 28, PL III), but the chromo- 
somes are still plainly distinguishable at the period of their greatest 
distribution. Anastomoses connect the various chromosomes. No matter 
how vacuolated or reticulated a daughter segment may become, a portion 
is always present, which is a denser central portion by which each chromo- 
some may be identified (Fig. 28, PL III). From this study it is certain 
that the chromosomes do not lose their identity, but persist as permanent 
structures in the reconstruction of the daughter nuclei of the first maturation 
division as they do in all resting stages. 
During the above described processes, the daughter nuclei increase in 
size. In the prophases of the homeotypic division the chromosomes again 
appear more condensed, occupy the same relative position, and have the 
same form as they entered the daughter nucleus. They lose whatever 
alveolar-reticulate structure they have and again appear as homogeneous 
bodies. Each daughter segment of each chromosome is, however, distinct 
in the prophases. P'ig. 29, PL III, shows the chromosomes lying free in the 
nuclear cavity just before the nuclear membrane breaks down. In Fig. 30, 
PL III, a pollen mother-cell wall is shown with two daughter cells in the 
process of division. One spindle shows the equatorial plate as seen from 
the side, and the other shows a polar view of the plate. Sixteen two-parted 
chromosomes are present. Fig. 31, PL III, represents an anaphase of the 
second division. Each chromosome is single. These single chromosomes 
form a univalent spirem (Fig. 32, PL III), during the reconstruction pro- 
cesses, as I have described for Thalictrum . I have also followed these 
chromosomes during the development of the young pollen grain, in which 
they appear as distinct, separate, univalent bodies or prochromosomes (Fig. 33, 
PI. Ill), such as are found in the vegetative cells of the anther wall. 
