6 BOTANICAL GAZETTE [JULY 
breadth, so that the line of longitudinal fission can be determined. 
The line of longitudinal fission is also indicated in other ways. 
Other chromosomes at this time are present in the form of short 
plates, some of which show slight indentations at the end, while in 
others longitudinal fission is complete, and a pair of rods is formed. 
During the process of shortening of the chromosomes, the 
greater part of the chromatin usually becomes massed at four 
definite points in the ring, or plates, or pair of rods. These 
denser masses of chromatin lie near the ends of the rods, or near 
the ends of each lengthened half of the ring or plate, and are 
connected by paler staining areas, the density of which varies in 
different rings. These four masses of chromatin, in the ring or 
in the rods as the case may be, form the tetrad. These rings 
and tetrads in Arisema triphyllum are very distinct, as much so 
as in certain animals. The two lengthened halves of the rings 
are usually more nearly separated along the line of longitudinal 
fission than along the line of transverse division, so that they 
quite readily separate. Each half of the ring is more or less 
crescent shaped, and the ends, instead of being rounded, are 
often quite regularly angular, presenting figures that frequently 
aid one in determining the orientation of the cleavage line. Up 
to this time the chromosomes still occupy their position around 
the periphery of the nuclear cavity, and, up to quite a late 
period, often show fragments of linin attached. 
The nuclear membrane now disappears, and the kinoplasmic 
threads, which are to form the spindle, enter and move the chro- 
mosomes upto the nuclear plate. The threads first radiate 
irregularly in all directions, but converge more and more at two 
poles as they gradually form the spindle. As this takes place, 
there seem to be two centers of force which lie at the poles of 
the spindle, and occasionally this is manifested a short time 
before the spindle is complete by radiations of kinoplasm about 
the poles in the form of rays, which suggests a centrosphere 
figure (jig. 74). This was observed very plainly in one case, 
and perhaps similar figures in other plants have led observers to 
interpret them as centrospheres., 
