34 Overton. — On the Organization of the Nuclei in the 
III. RlCHARDIA AFRICAN a. 
The Monocotyledons so far as at present described are not found to 
show prochromosomes in all stages of the resting vegetative and germ 
nuclei. I find, however, that in Richardia africana the prochromosomes 
are constantly present as visible, well-defined bodies, which correspond to 
the chromosomes in number as I have described for Thalictrum purpurascens 
and Calycanthus floridus. 
I have investigated the pollen mother-cells of the common Calla 
{Richardia africana). The material, which was obtained from greenhouse 
plants, was fixed in Flemming’s fluid. The chromosomes in this plant have 
been traced throughout the various stages in the development of the pollen 
mother-cell, in which they persist as permanent structures similar to those 
of Thalictrum and Calycanthus. Richardia is especially interesting on 
account of the early appearance of the longitudinal splitting of each com- 
ponent of the bivalent chromosomes. The material is also especially 
favourable as showing the permanence of the chromosomes during the 
reconstruction stages of the daughter nuclei, and the prophases of the 
homeotypic division. 
The nuclei of the young pollen mother-cells of this plant are not as large 
as those of Calycanthus , but are considerably larger than those of Thalictrum. 
The pre-synaptic nuclei of Richardia show essentially the same conditions 
as have been described for Calycanthus. Fig. I, PI. Ill, shows a pre- 
synaptic nucleus, with the prochromosomes well defined. The linin frame- 
work is also very apparent, but the parallel arrangement of the linin 
connecting intervals, which is so markedly present in Thalictrum , is not 
so easily made out in Richardia. 
The structure of the prochromosomes is shown in Figs. 9^-9 c, PI. III. 
The chromatin is densely massed (Fig. 9 a, PI. Ill), or may be somewhat 
spread out along the linin intervals (Fig. 9 h, PL III) so that a row of 
chromatic groups may be distinguished. The chromatic groups are also often 
scattered along the linin threads, being thus somewhat separated from each 
other (Fig. 9 c, PI. III). In this stage the chromatin and linin intervals are 
frequently parallel. 
Figs. 2 and 3, PI. Ill, represent the beginnings of the synaptic con- 
traction, which condition is much more advanced in Fig. 3 than in Fig. 2. 
There is a distinct parallel arrangement of elements, but the limits of the 
prochromosomes are not easily made out (Fig. 2, PI. III). In Fig. 4, PI. Ill, 
the contraction is still more complete. Fig. 5, PI. Ill, represents a complete 
contraction stage, in which the elements are shown massed together much 
more compactly than in either Thalictrum or Calycanthus. In the complete 
contraction stage the prochromosomes are still plainly visible, arranged in 
parallel pairs. The nucleole may or may not be entangled in the synaptic 
