Acer negundo , Z., and Staphylea trifolia , Z. 119 
radially loops and straight portions. In many cells in Lilium this arrange- 
ment of radiating loops and straight portions of the spireme from the 
central knot occurs with almost the regularity of a diagram. 
In Acer negundo there is present the feature that represents the second 
contraction, but it does not appear with the regular radiating loops, save, 
perhaps, in rare cases. During this rearrangement the spireme loses, as 
a rule, its more regular course and uniform thickness. It shows a tendency 
in many cells to become relatively thick in some places and attenuated in 
others. The loops and turns become shorter and so arranged that a picture 
of the whole nucleus, or a thick section of the same, does not present the 
regularity of Fig. 12. The most regular appearance of the spireme observed 
just before the segmentation into the chromosomes is represented in Fig. 13. 
Here certain parts of the spireme extend in straight stretches from a some- 
what centrally located entanglement, while other parts form longer or 
shorter loops, which may be variously twisted or kinked. The stage fol- 
lowing Fig. 13 is shown in Fig. 14. In this we see that the spireme is at 
least partly segmented. This nucleus shows a much greater regularity in 
the arrangement of the chromatin than is usual, and I have selected such 
nuclei as illustrations for the reason that the parts may be clearly and 
definitely made out. It is evident that the spireme has segmented into 
pieces that are either straight or in the form of loops. Closely following 
upon the stage of Fig. 14 is that of complete segmentation shown in 
Fig. 15. The spireme, which gives no evidence of being double or longi- 
tudinally split, has segmented transversely into a number of pieces that were 
previously joined end to end to form that spireme. These pieces (Figs. 15, 
16, 17, and 18) are in the form of straight rods, closed or open rings, or 
loops. The parallel sides of the loops may be twisted about each other, 
sometimes tightly and closely, sometimes loosely, forming figure 8’s, as has 
been described for other plants. Each loop, ring, U, or 8 represents 
a bivalent chromosome made of two somatic chromosomes which have not 
separated at the extremities representing the bend of the loop. A loop or 
a ring is, therefore, a continuous piece of the spireme composed of two 
somatic chromosomes (Figs. 17, 18). Figs. 17 and 18 are tangential views 
of nuclei, while Figs. 35 and 16 are more nearly radial sections. A ring is 
formed when the two halves of a loop curve away from each other equally, 
leaving the free ends closely juxtaposed or touching, or even slightly over- 
lapping, each other. The formation of a U from a piece of the chromatin 
spireme is self-explanatory. Of course, a ring may not necessarily owe its 
form to a previously looped portion of the spireme. For example, the 
large ring in Fig. 17 may have arisen from a loop, the free ends of which 
have touched end to end by the bending of the two sides, while at the point 
of bending of the loop the other ends of the two somatic chromosomes have 
tended to pull apart ; or two curved somatic chromosomes may touch at the 
