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AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
lie against one another (figs. 19,20). They do not twist around one an- 
other, however, to form the characteristic condition known as strepsinema. 
When the cHmax of condensation has been reached, the loops are some- 
times so short that they are barely visible beyond the edge of the central 
mass (fig. 21). In practically no case, however, are they entirely lost 
sight of. Throughout the whole of this period at least some of the loops 
are in evidence, and it seems certain that they form the bivalent chromo- 
somes which are soon to emerge from the contracted mass. 
The nucleolus is usually not involved in this condensation. During 
the second contraction it ordinarily retreats again to the nuclear membrane, 
where it begins to flatten out once more. It still shows as clearly as ever 
the black-staining endonucleolus (figs. 18-20, 23). 
It is important to notice that there is almost no indication of the oc- 
currence of any kind of split in the spireme during this process of con- 
traction. In only a very few instances have I found any trace of it, and 
these were in poorly fixed cells. It is possible that about or before this 
time the spireme begins to divide lengthwise in preparation for the homoeo- 
typic division, and that this split occasionally shows. If the spireme were 
bivalent in nature, however, we ought to find at this stage, when the chro- 
mosomes are preparing to separate from each other, that the spireme is 
everywhere splitting into two threads. I have been unable to find evidence 
that such a splitting occurs. The thread is constantly single. 
As the loops become shorter and thicker, the first indications of the 
approaching cross-segmentation of the spireme make their appearance in 
the form of constrictions (figs. 16, 19, 21). A constriction may be found 
at the distal end of the loop, in which case each side of the loop represents 
a chromosome. In some cases a single chromosome makes up the whole 
of the distal portion, its ends being found part way down the sides (fig. 
19). Such a loop might be made up of two, or of more than two chromo- 
somes. The distal chromosome might be attached at both ends to the 
same chromosome, the middle part of which is hidden in the central mass, 
or the ends might be in contact with different chromosomes. We shall 
see shortly that the latter condition is probably always found in the case 
of one of the loops. 
That the chromosomes are placed end to end in the spireme which 
makes up these loops is indicated by the fact that the individual loops 
may be traced entirely through the second contraction stage without 
showing any longitudinal splitting, emerging at the end of the period, each 
as a pair of chromosomes which are attached to each other by their ends. 
There is little doubt in my mind but that the segmentation which appears 
in the loops as these are contracting represents the separation of univalent 
chromosomes and not of bivalent ones. 
Diakinesis. Up to this point we have been dealing with the spireme 
as a whole. During the earlier stages of prophase the thread system has 
