558 MorrieER AND NOTHNAGEL: CHROMOSOMES OF ALLIUM 
who hold to the doctrine that two spirems fuse side by side during, 
or prior to, synapsis and who deny that the somatic chromosomes 
are arranged end to end ina lineal series to make the continuous 
hollow spirem. These authors ignore the fact that three or more 
threads fuse in the formation of the spirem from the net as well 
as only two, and as will be pointed out in a subsequent paragraph, 
they omit from consideration and from their series of figures the 
most difficult and perhaps the most important steps in the forma- 
tion of the bivalents from the hollow spirem. 
FROM SYNAPSIS TO THE BIVALENTS 
The stage of FIG. 4 passes directly into the closely contracted 
mass of FIG.5. While the chromatin is still in this state, the thread 
gradually shortens and thickens into a heavy cord. Even before 
an appreciable loosening up of the synaptic ball it is readily seen 
that a thick spirem, or cord, is forming from the slender thread, 
and, as soon as the contracted mass loosens (Fic. 6), the correct- 
ness of this interpretation is beyond doubt. We have in our 
preparation transitional stages between FIG. 5 and 6, but it was 
not deemed necessary to include these in the series. The thick 
cord thus developed now becomes distributed throughout the 
nuclear cavity. In Allium it is relatively thick, apparently 
rather uniform in structure, though sometimes lumpy, and in 
many cases numerous delicate threads extend from the spirem 
to the nuclear membrane or between adjacent or parallel portions 
of the cord (Fic. 7, 8). A nucleolus is usually present. At this 
stage a longitudinal split may be sometimes seen, but this phe- 
nomenon is rather the exception than the rule (Fic. 8). This 
fission always closes up and the two halves become so closely 
applied or fused that the double nature of the thread, if really 
present, is completely concealed before any indication of cross 
segmentation is discernible. 
Following the stage of the loose hollow spirem, the same 
undergoes a rearrangement before transverse segmentation, 
which results in a twisting, looping, and an entangling of its parts. 
This phenomenon found in the lilies and in other plants is known 
as the second contraction. In the lilies there is a central knotted 
or entangled portion of the spirem from which extend somewhat 
