Graham . — Nuclear Division of Preissia commutata . 673 
matin bodies on it are very distinct. The loosening of the synaptic knot 
and the emergence of the spireme continue until the spireme is uniformly 
distributed throughout the nuclear cavity (Fig. 6). The spireme is at this 
stage still quite slender and its appearance is very different from the 
leptonema spireme. The chromomeres are of the same size and form and 
are placed at almost equal distances from one another. They become more 
prominent as the spireme thickens (Fig. 7). A post-synaptic spireme in 
Liverworts has been described by Davis (’ 01 ) in the spore mother-cell of 
Pellia epiphylla , where it appears as a delicate, closely wound spireme. The 
spireme shown in his illustration is evidently in the same stage as that in 
Fig. 6 of the present work. The nucleolus in Preissia commutata, however, 
is not vacuolated at this stage, while in Pellia epiphylla Davis (’ 01 ) found 
the nucleolus vacuolated. 
There is a gradual shortening and thickening of the spireme (Figs. 8, 9) 
which results in the formation of what is sometimes called the ‘ pachynema ’ 
spireme. At this stage the width of the spireme has increased very much 
(compare Figs. 6 and 9). 
From this time there is another contraction of the spireme. It contracts 
away from two opposite sides of the nucleus, so that it occupies a rather 
broad plane, extending entirely across the nucleus. The loops of the 
spireme do not have any definite arrangement (Figs. 8, 9), but the entire 
spireme is drawn rather closely together across the diameter of the nucleus. 
Some of the loops touch the nuclear membrane (Figs. 8, 9). This stage is 
the second contraction described by Farmer and Moore (’ 05 ). However, in 
Preissia commutata it occupies, as has been said, a broad plane extending 
entirely across the nuclear cavity and does not extend in all directions in 
the nuclear cavity with large spaces between the contracted portions, as is 
the case during the second contraction in Lilium candidum as described by 
Farmer and Moore (’ 05 ) and in Lilium speciosum by Gregoire (’ 07 ). Many 
sections with spiremes in the same general position as those shown in Figs. 8 
and 9 were obtained, which indicates that this stage lasts for some time in 
Preissia. 
When the spireme is entering upon the second contraction, it begins to 
split longitudinally throughout its entire length. Some portions of the 
spireme are so situated that the split is plainly seen (Figs. 8, 9). The 
chromomeres that are so prominent in the earlier prophases (Figs. 4, 5, 6, 7) 
are now not recognizable (Figs. 8, 9). Fine short threads project from the 
margin of the spireme, giving it a somewhat jagged appearance. 
The spireme is always contracted about or near the nucleolus. At this 
stage the centre of the nucleolus stains less deeply than the periphery. 
This may be due to the method of staining or to the chemical changes that 
have taken place in the nucleus. It is certain, however, that at this stage 
the nucleolus is not vacuolate, and its size and shape remain the same as in 
