50 Overton . — On the Organization of the Nuclei in the 
Probable Separation in Time of Association and 
Interchange. 
It is quite apparent from a survey of the recent literature of reduction 
phenomena that there is a strong tendency to the view that the association 
in pairs of the homologous chromosomes and an actual interchange or 
influence, in so far as any may occur, preparatory to reduction division may 
be widely separated phenomena. The view is quite general that the possible 
interchange is associated with synapsis. 
Although Juel (’ 05 ) believes that it is not necessary for chromosome 
union and fusion to occur uniformly at the same period in the maturation 
of the germ cells, I believe the facts of reduction as we now know them 
indicate a uniformity of the phenomenon of actual fusion in point of time. 
I am also inclined to agree with Rosenberg (’ 05 ) and Juel (’ 05 ) that the 
actual fusion occurs in the plants which I have studied during the early 
spirem stage rather than during synapsis or pre-synapsis. 
Although the prochromosomes have always been found in parallel pairs 
during pre-synapsis, as is shown in Figs. 2-8, PL I, 1-3, PI. II, and 1-3, 
PI. Ill, the members of each pair are no more closely united during this 
period than they are in the somatic or pre-meiotic cells. Compare Figs. 9-1 1 , 
PI. I, 4-6, PI. II, 4-7, PI. III. During the early post-synaptic stages there 
is a close association of the homologous components of the pairs, so that 
each univalent chromosome is somewhat difficult to recognize. 
In Fig. 12, PI. I, Thalictrtim purpurasce 7 is, the post-synaptic spirem is 
shown as just beginning to be distributed in the nuclear cavity. At this 
stage the two parallel portions are still quite distinct. In Fig. 13. PI. I, which 
represents a portion of a much more distributed spirem, the univalent parts 
are very close together. Fig. 14, PI. I, shows that the univalent portions of 
a completely distributed spirem are very much more closely associated than 
they are during pre-synaptic stages. Figs. 16-19, PL I, show how very 
closely the parallel portions are associated during post-synaptic and diaki- 
netic stages. In Fig. 6, PL II, the synaptic contraction in Calycanihus 
floi'idus is shown as loosening up. Here the parallel portions are more 
closely associated than in the earlier stages (Fig. 5, PL II). Figs. 7 and 8, 
PL II, show the parallel portions of the distributed spirem as very closely 
associated. That the parallel portions of the bivalent post-synaptic spirem 
are more closely associated than during pre-synaptic stages in Richardia 
africana is shown by Figs. 8-1 1, PL III. 
From my own observations it is evident that there certainly exist in 
pre-synapsis parallel pairs of chromosomes or chromosome primordia, which 
do not fuse during the synaptic stages, but become most intimately associ- 
ated during the post-synaptic spirem stages. If symmixis is to occur, it is 
