672 Graham.— Nuclear Division of Preissia commutata. 
in which it is possible to trace a continuous thread for some distance (Fig. 2) 
is replaced by a slender thread, the whole reticulum having been converted 
into a slender thread (Fig. 3) which is called leptonema by some authors 
(Winiwarter (’01), Gregoire (’07), and others). From the frequency of its 
occurrence in sections at this stage of prophase, it is evident that the 
leptonema spireme is formed a considerable period before synapsis. In this 
figure many threads may be seen lying side by side. This suggests a pairing 
of the threads. The threads of many of these pairs are more slender than 
others which lie singly. It would be interesting to know if these stouter 
single threads are formed by the side-by-side union of a pair of the slender 
ones, or by such a close approximation that the line of division between 
them cannot be seen. The pairing of these threads suggests the condition 
of the spireme in Osmunda regalis , Allium fistulosum , &c., described and 
figured by Grdgoire (’07) as ‘ noyaux zygotenes \ Gregoire (’07) does not 
find a continuous spireme — the chromosomes or gemini arise as long slender 
threads ; while in Preissia commutata my preparations in early prophase 
have the appearance of the spireme being a continuous thread. Because of 
the very small size of the nuclei and the great length of the thread it is 
difficult to speak with certainty. There was no evidence, however, that 
prochromosomes such as are described by Strasburger (’05) in Galtonia 
candicans , by Miyake (’05) in the same plant, and by Overton (’09) in 
Thalictrum purpurascens , and by others, were present in the spore mother- 
cell of Preissia commutata . The appearance is that of a spireme that persists 
for a considerable time. 
The spireme next enters into synapsis (Fig. 4). In the synaptic knot 
there is evidence of the persistency of the spireme, as the appearance of the 
knot in Fig. 4 plainly shows, but it is so tightly drawn together that it 
cannot be followed throughout its length. In the synaptic knot there are 
many chromatin bodies of equal size and shape. These bodies are extremely 
prominent and are always present at this stage of the prophase, but they 
are arranged in rows or in the form of a spireme. These prominent chromatin 
bodies of equal size and shape in the synaptic knot are very suggestive of 
the condition found by Strasburger (’05), Miyake (’05), and Overton (’09) in 
seed plants. At this phase, according to these investigators, the prochromo- 
somes, or gamosomes, pair. In Preissia commutata there is no evidence in 
the synaptic knot that these chromatin bodies come in contact in pairs. It 
may be, however, that during synapsis the pairs of threads described above 
may be brought into closer approximation and actually fuse, thus producing 
this stout spireme with the chromatin masses situated at quite regular 
intervals. The nucleolus may be included in the synaptic knot or lie by 
its side. 
As the spireme emerges from synapsis, there is a general loosening of 
the entire structure (Fig. 5). At this time it is quite slender and the chro- 
