MOotTTIER AND NOTHNAGEL: CHROMOSOMES OF ALLIUM 561 
spindle fibers, each is bent at the place of attachment and a ring 
results. In FIG. 16 some of the rings are seen from the edge while 
others have their flat sides turned toward the observer, In many 
of these rings it is still very evident that they were loops of the 
spirem as shown above. However, the open or closed ring is not 
the only form seen in the spindle stage. Sometimes the bivalents 
appear as two straight or crooked rods attached at or near the 
ends to the fibers, or X- and Y-shapéd forms may appear. 
One of the most conspicuous phenomena in the whole mitotic 
process of this species, and one which is very significant when 
viewed in the light of the kinetic processes involved in mitosis, 
is the shape of the chromosomes just before the appearance of the 
multipolar spindle and at the stage of the mature spindle (Fig. 13, 
16, 17); In FIG. 13 the members of each bivalent, or at least 
the large majority of them, are tightly twisted about each other, 
while in FIG. 16 and 17 they appear just as uniformly as open 
rings. The question arises: what kinetic forces are responsible 
for the twisting in FIG. 13, and what for the condition of FIG. 17? 
A discussion of this interesting question would extend far beyond 
the limits of this paper, and we shall merely venture the opinion 
that neither magnetic nor osmotic activities seem applicable to 
the phenomena under consideration. 
During metakinesis, that is, just at the instant when the 
segments are separated, each shows iis longitudinal fission. 
Each half-ring, which is made into a U by the pull of the spindle 
fibers, is now a double U. Frequently just before metakinesis 
this longitudinal fission can be seen when the free ends of the 
bivalent are turned directly toward the observer (Fic. 18). In 
FIG. 19, an anaphase, the double U-like nature of the daughter 
segments is clearly shown. It may be remarked in passing that 
the large size and elongated form of the chromosomes of the 
mature spindle, and the fact that the halves of the U’s and v’s 
tend to separate from each other during the anaphase, make 
counting perplexing and uncertain, in spite of the large size and 
small number. 
The shape and position of the various chromosomes as they 
pass to the poles seem to speak strongly in favor of a pull being 
exerted by the spindle fibers, which are in reality fine colloidal 
