Pollen Mother-cells of Certain Plants. 25 
connected with the cytoplasm I have been unable to determine. In this 
plant I have not discovered any relation between the position of the synaptic 
mass and the side of the nucleus nearest the cell wall as observed by 
Marquette (’07 and ’08). In some cases the nucleus lies close to the cell 
wall, and the mass may be on this side (Fig. io, PI. I), and again the reverse 
is true. There is no apparent polarity in these cells. 
In my studies on Campanula grandis , Helleborus foetidus , and Podo - 
phylhim peltatum , I found that the young post-synaptic spirem began to 
extend into the nuclear cavity in the form of more or less regularly arranged 
loops, each loop being connected through or with the nuclear membrane by 
one or more finely-beaded, delicate linin threads, which appear by their 
contraction to aid in the distribution of the post-synaptic spirem. Little by 
little these loops extend into the nuclear cavity, and it is then that the 
bivalent character of the spirem becomes very evident, its halves often 
diverging widely from each other. In these plants at this stage the number 
of these loops bears no constant relation to the number of the chromosomes, 
although in certain cases these loops correspond in number to the number of 
chromosomes. At that time I was unable to follow the behaviour of the 
post-synaptic chromosomes of Thalictrum and Calycanthus for reasons 
already mentioned. 
In Thalictrum I have been unable at any stage in the development of 
the pollen mother-cells to find a continuous chromatic spirem. The linin 
and chromatin pass as distinct elements into the synaptic contraction. 
There is then a general loosening up of this mass. Each prochromosome 
seems to lengthen somewhat, suggesting a distribution of its chromatin along 
the linin (Figs. 12 and 13, PI. I), but forming no continuous chromatic 
spirem. The spirem at this stage is simply a continuous bivalent linin 
thread with the chromatin of the parallel prochromosomes somewhat more 
distributed than in earlier stages (Fig. 13, PI. I). Figs. 14, 15, PI. I, show 
the chromatin and linin as still distinct. We see, then, that in this plant the 
prochromosomes may be traced through the synaptic contraction as 
individual bodies, which are certainly the same as those found in the post- 
synaptic spirem. Any regular folding of the thick spirem to bring these 
bodies together is absolutely impossible. They are associated in parallel 
pairs during pre-synaptic stages, and remain so until they assume the form 
found in the pachynema stages. 
On account of the limits of the chromosomes being always visible, 
I have been able to follow the exact history of each univalent element from 
its entrance into the heterotypic spirem until the diakinetic stage. Fig. 14, 
PI. I, shows how the bivalent chromosomes are arranged and distributed in 
the spirem. The chromatin of each univalent chromosome is still somewhat 
distributed along the linin as has been described above (Fig. 13, PI. I), but 
the line which separates the two is still very apparent. The univalent 
