Pollen Mother-cells of Certain Plants. 35 
mass as is shown in Figs. 5 and 6 , PL III. The synaptic contraction is 
a gradual process as in the other plants studied. 
Later stages of the synaptic contraction are shown in Figs. 7 and 8, 
PI. Ill, in which the chromatin is grouped in masses on parallel linin 
threads, but it soon begins to spin out along these threads, until an almost 
complete homogeneous spirem is formed in synapsis (Fig. 10, PL III). 
Figs. 9 a-g c, PI. Ill, illustrate the behaviour of the chromatin as it passes 
through synapsis. In Fig. 9 c, drawn from a late synapsis stage, a spirem 
is beginning to be formed, which at first glance is homogeneous or 
continuously chromatic. This condition just immediately precedes the 
redistributed spirem (Fig. 10, PI. III). As in Thalictrum and Calycanthus , 
I have been unable to find distinct, regularly-arranged chromosomes in the 
spirem as is often described for Lilium and Allium. Fig. 11, PI. Ill, shows 
a completely distributed post-synaptic bivalent spirem, and needs no especial 
mention. The two univalent portions of such a double spirem are distinctly 
visible at this stage (Fig. 12 a, PI. III). The bivalent spirem much resembles 
that of Campanula grandis , or the lily-type, which I have described in my 
former paper. Although the chromosomes appear so evenly distributed in 
the spirem, I have been able to distinguish the individual limits of the 
chromosomes by the fact that the places in this spirem where two adjacent 
chromosomes unite end to end are always marked by thinner, less chromatic 
regions, as is shown in the above figures. I have been unable to discover 
the existence of a second synapsis, or any regular arrangement of the spirem 
into loops corresponding to the number of the chromosomes, as has been 
described for Lilium and Podophyllum . The post-synaptic spirem remains 
distributed in the nucleus until its segmentation. Since the chromatin of 
the chromosomes is more distributed along the linin threads of the spirem, 
the segmentation of the spirem is exactly like the process described for 
Thalictrum and Calycanthus , the details of which are represented in Figs. 
12 a and 12 h, PL III. Since the chromosomes of Richardia are larger than 
in the other two plants, some phases of the process might possibly be 
interpreted as due to bending, but a careful study shows that the segmen- 
tation and consequent separation of each univalent portion of the spirem to 
form the corresponding univalent portions of the diakinetic chromosomes 
does not occur at the points of bending (Figs. 12 a and 12 b, PL III). The 
parts of the bivalent chromosomes often become twisted about each other 
(Fig. 12 £, PL III). Just after the segmentation of the spirem the chromo- 
somes lie rather uniformly scattered in the nuclear cavity (Fig. 13, PL III). 
Figs. 14^-14^, PL III, are drawings of single chromosomes taken from 
diakinesis, and show the characteristic shapes of the chromosomes. The 
usual arrangement is that of parallel double rods (Figs. 14 a and 14 
PL III), but there are some exceptions (Figs. 34 c and 14 d, PL III). 
Fig. 15, PL III, represents a late diakinetic nucleus just before the nuclear 
