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396 AMERICAN JOURNAL OF BOTANY [Vol. 9, 
of such long threads cannot remain in such a small space unless the threads 
are very sharply and frequently bent and twisted. There is a tend- 
ency to resist this excess of bending, to straighten out, and hence the 
unfolding. 
The nucleolus, which at the beginning of synizesis moved over against 
the nuclear membrane, becomes by mid-synizesis not only flattened but 
much spread out and quite often assumes the shape of a horseshoe or 
doughnut. That it is comparatively empty is shown by the staining and 
by the fact that an endonucleolus now stands out very clearly within it 
as a black-staining, spherical little body. This body makes its first ap- 
pearance in early synizesis and remains a constant feature of the nucleolus 
until the time of the disappearance of the latter during diakinesis (fig. 11). 
Synizesis is, then, the time during which transition is made from a 
thin-threaded reticulum with scattered chromatin particles to a thick- 
threaded spireme. This transition does not appear to be brought about 
by the parallel fusion of two separate thread systems, but by a process 
which consists largely of the contraction of certain threads and the absorp- 
tion of their contents into the body of other threads, a process which 
involves only occasional parallelisms. It seems, also, that the total amount 
of chromatin on the threads is greatly augmented during this process, 
and it is not unlikely that the extra chromatin has been brought out of the 
nucleoli and distributed along the network. 
The Open Spireme. The unfolding of the synizetic knot is gradual. 
It is accompanied by little further thickening of the spireme. The large 
irregular accumulations of chromatin which were formed in the center of 
the knot during synizesis are dwindling, though the threads at the center 
are usually found to be somewhat thicker than the rest of the network 
through the whole of the open spireme stage (PI. XXV, fig. 12; PI. XXVI, 
figs. 13-15). 
Judging from the frequency of its appearance, the open spireme stage 
is one of fairly long duration. The threads are long and evenly distributed 
through the nucleus (fig. 14). They frequently show a distinct and regular 
beading. It is often possible to trace a single thread for a long distance 
as it winds and twists through the nucleus. Here and there it joins with 
other threads, the whole system constituting not a single coiled or twisted 
thread but a loose reticulum. Ordinarily it is not possible to locate any 
threads with free ends. 
During the open spireme stage the threads are characteristically single 
and unsplit. Wherever they are prominently beaded, the beads are found 
to be arranged in a single row, stretching quite across the thread and show- 
ing no sign of division. Once in a while one may find in late synizesis 
a lingering trace of parallelism, but in the open spireme we rarely have 
anything to indicate that the thread might be by nature double. Occa- 
sionally two parts of the spireme may lie rather close together, and the 
