The individuality of the chromosomes and their serial arrangement, etc. 123 
phases of the somatic division, and yet witli some striking similarities. 
In both there is a marked early growth of the nucleus. In somatic pro- 
phases the chromosomes maintain a rather constant form. In preparation 
for synapsis, however, the chromosomes change their shape and the 
chromatin is drawn out into a delicate thread of considerable length, 
a condition to which there is nothing comparable in the somatic divisions 
of the plant and which is plainly an entirely new condition of the chro- 
matin material, a point which is discussed fiirther on. 
The synaptic stage with the changes immediately preceding and 
follomng it, evidently lasts for some time, perhaps several days. As 
the knot loosens up we find a thick continuous spirem which appears as 
one soüd homogeneous thread. The loosening continues until the thick 
spirem (pachyneme) is distributed quite evenly in the nuclear cavity 
where it is variously twisted about as is shown in figure 23. The stages 
of this loosening can be followed in the greatest detail, but there is no 
\üsible evidence regarding the mechanism of the process. At this stage 
no longitudinal spht can be discerned in the thick spirem and through- 
out its entire length there appears no indication of the limits of the 
individual chromosomes. 
I have not found Intermediate stages between the spirem Just de- 
scribed and diakinesis and caii not at this time contribute anything further 
to the question of the origin of the paired chromosomes as they appear 
in diakinesis. The bivalent chromosomes of dialdnesis are sharply de- 
fined (fig. 24). There is good evidence that here, also, they are arranged 
in a continuous series. The Suggestion is strong that the thick spirem 
was double and that the diakinetic pairs have arisen by a contraction 
in length of the material of each chromosome. At the earliest stages of 
diakinesis it is to be observed that the chromosomes have not completely 
rounded up, but are drawn out into thread-like extensions which connect 
the individuals of successive pairs into the double series thus suggesting 
that, as noted, the pairing is due to the parallel arrangement of two series 
of chromosomes. 
In diakinesis, as has been almost universally agreed, the pairs of 
chromosomes lie in the periphery of the nuclear cavity against the nuclear 
membrane. This position is similar to that of the univalent chromosomes 
as described above during the early prophases of the somatic divisions 
(compare figure 24 with 6). This stage in Carex acuta was figured by 
JuEL (1900, fig. 30), but he does not show the doubhng of the chromo- 
somes which is so conspieuous in my preparations. The chromosomes 
are roughly eUiptical with the sides which are in contact somewhat flat- 
