558 Davis . — Cytological Studies on Oenothera. I . 
are loops of the now very much shortened and thickened spirem, and 
there seems no reason to doubt that a structural organization is present 
no matter how compact and homogeneous the synaptic knot may 
appear. 
The chromatic material emerges from synapsis by a general loosening 
up of the elements which compose the contracted knot, and then for the 
first time it becomes evident that the chromatin has taken the form of 
a group of rings. Later the rings may be easily counted, the number 
being seven, which is half the number of chromosomes present in the 
vegetative or sporophytic mitoses. These become the seven bivalent 
chromosomes characteristic of the heterotypic mitosis. 
The origin of certain of the rings from chromatin loops which extend 
from the synaptic knot appears very clear in such preparations as have a 
synaptic knot of the looser type, such as is illustrated in Figs. 20 and 23. 
In these cases each loop is transformed directly into a chromatic ring, and 
frequently three or four of the seven rings composing the group arise from 
such loops (Figs. 24, 25, and 26). The remainder of the rings in such 
nuclei are derived from the contracted portion of the synaptic chromatin, 
where the shortened and thickened coils of the spirem are so closely 
pressed together that the elements cannot be distinguished. Rings that are 
formed from loops are generally at first exceptionally large (Figs. 25, 26, 
and 29), but they rapidly grow smaller by evident condensation as the 
nucleus prepares for the heterotypic mitosis. 
It was impossible with the technique employed to trace with exactness 
the development of the rings from synaptic knots of the dense much- 
contracted type, such as are shown in Figs. 21 and 22. These rings are 
organized when the chromatin is in the contracted state, and appear fully 
formed with the loosening up of the synaptic knot as that structure emerges 
from synapsis (Fig. 27). Such rings are readily distinguished from those 
formed from the free loops because of their small size and more regular 
and compact form (Figs. 27 and 28). They are at first closely grouped 
around the nucleolus (Fig. 27), but later become more generally distributed 
in the nuclear cavity (Fig. 28), illustrating the phase termed diakinesis. 
Frequently two or three of the rings become separated early from the 
others, and consequently lie freely in the nuclear cavity, while the remainder 
are still so closely massed in a group that their outlines cannot be clearly 
followed. Such free rings are very conspicuous and may be readily 
studied (Fig. 28). 
It is certain that the fully developed rings are generally completely 
closed. It is exceptional to find a ring open on one side, but such are 
sometimes present. The rings are, however, not uniform in density, but 
are generally thinner at one or two points. These conditions become much 
more evident as a nucleus approaches metaphase of the heterotypic 
