30 Overton. — On the Organization of the Nuclei in the 
stage of the ripe pollen. The prochromosomes are visible as univalent 
structures in the pollen grain and are arranged in a single series (Fig. 37 
PL I). There is every reason to believe that, since the chromosomes 
appear as unreticulated bodies in the mature pollen grain, as well as in all 
preceding nuclei, they probably persist as permanent structures in the nuclei 
of the generative cells. 
II. Calycanthus floridus. 
In my former study of Calycanthus floridus I presented evidence to 
show that the chromosomes were everywhere permanent structures, being 
represented both in resting somatic and germ nuclei by chromatic 
aggregation or prochromosomes, just as in Thalictrum. I was, however, 
at that time unable to trace these bodies through all the stages of the 
development and division of the pollen mother-cells of Calycanthtis. 
I am now able to present the then missing stages, and to show 
that the chromosomes retain their permanence during all stages, as in 
Thalictrum. 
The pre-synaptic nucleus of Calycanthus floridus resembles that of 
Thalictrum purpurascens in that there is a distinct parallel arrangement 
of chromatin and linin elements, as I have described in a former paper. 
The chromatin is usually massed into definite bodies (Fig. 1, PL II). The 
prochromosomes are arranged in pairs, with parallel linin intervals, as has 
already been described for. Thalictrum purpurascens. These pre-synaptic 
heterogeneous spirems are connected by cross linin strands, which are 
usually much more numerous and finer or thinner than the linin intervals 
of the spirem. There is a tendency in this plant for many of the pro- 
chromosomes to lie close to the nuclear membrane. The nucleus is much 
larger than in Thalictrum purptirascens and the chromosomes are fewer in 
number (24), so that the nucleus presents a much more open appearance. 
In some cases the chromatin of the prochromosomes is not entirely massed 
at definite points (Fig. 2, PL II), but may be somewhat spread out along 
the linin threads, a condition which I have never observed in Thalictrum 
purpurascens. The parallelism of the pre-synaptic elements is maintained 
whether the chromatin is much or little distributed (Figs. 1 and 2, PL II). 
The prochromosomes are, however, perfectly distinct in such nuclei, and 
may be easily counted. The parallel linin threads are also distinct in such 
cases. If the chromatic substance of the prochromosomes were still more 
distributed along the parallel linin threads, so that the limits of the 
individual prochromosomes could not be distinguished so as to form an 
almost continuous chromatic spirem, we should have a structure essentially 
similar to that of the onion, as I have already described in a previous paper. 
Podophyllum peltatum shows a spirem between the lily-type and that 
of Calycantlms and Thalictrum. 
