6 -- BOTANICAL GAZETTE [JANUARY 
necessarily lie side by side with those in the other; in other words, 
there is no uniformity in the relative position of the knots in the two 
parallel threads. : 
The double threads, having such a structure and traversing the 
nuclear cavity in various directions, now become tangled in a mass 
at one side of the cavity in the condition called synapsis (jig. 9). 
Synapsis is not an artifact, but a normal stage of prophase, which 
may be observed in living material. The position of the nucleolus at 
synapsis is variable; sometimes it lies at a distance from the synaptic 
mass, but more often it is caught in the tangle. Its form is generally 
spherical. 
Very frequently it occurs that in the tangled mass many parts of 
the threads are seen converging to that point where the mass is in 
contact with the nuclear membrane. A similar condition is described 
by GREGOIRE in O. regalis (5). In this case, some of these parts are 
continuous with the other parts, and evidently they do not yet repre- 
sent chromosome primordia already disconnected and independent. 
The chromagin structure of the double threads, as seen in the 
presynaptic stage, is kept throughout this synaptic condition; the 
two members of the pair may come into closer association in some 
places than before, but the duality is never lost, even in the culmina- 
tion of synapsis (fig. 10). This means there is no actual fusion of 
the two threads. 
The synaptic mass then begins to disentangle and the double 
threads again assume a position traversing the entire cavity, the two 
being always clearly in close association. Each element of the 
double thread then shortens. During the strepsinema stage some 
parts of the double threads gather somewhat at a part of the 
nuclear cavity, looking like a second contraction stage (fig. rz; in 
which only a part of the threads are represented, as they are seen in 
one focus). Soon after this stage the double threads rapidly shorten 
and thicken, and finally in a diakinetic stage there are formed 22 
bivalent chromosomes (fig. 12). In some cases the two elements 
of each bivalent chromosome remain in close contact, but in other 
cases they become somewhat separated, and, as a consequence, there 
are produced the various-familiar aspects of bivalent chromosomes. 
After the formation of the bivalent chromosomes, the shortening 
