A STUDY IN CHROMOSOME REDUCTION. 613 
spireme. All the facts revealed point to the conclusion that there are as many 
spiremes as there are chromosomes. It naturally follows that the looping method of 
reduction cannot occur in these plants. 
Returning now to the Smilacina series, we must take note of certain other features 
of the bivalent chromosomes. In the early stages of the prophase, before the spiremes 
have united in pairs, the great leneth of the chromatic filaments renders it impossible 
to obtain an exact count of the threads present. The spiremes, however, are sufficiently 
independent of one another to allow of a rough estimate. Repeated counts of this 
nature make it quite certain that the number is a large one. The number, for instance, 
in the stage shown in fig. 15 is much greater than that in fig. 24. As soon, however, 
as the larger number has been reduced by half as a result of the pairing, and this being 
followed by a marked condensation, the number of bivalent chromosomes may be 
estimated with a fair degree of accuracy. Numerous counts were made from sections’ 
like that shown in fig. 24, which is almost median. The highest number found was 
fourteen, and this was so frequently found both at this time and later (fig. 33), that 
this is probably the characteristic haploid number for the species. 
Another feature of importance to note in connection with the chromosomes is their 
difference in size. In the spireme stage, before reduction occurs, the difference in the 
length of the chromatic filaments is not very noticeable. ‘The threads are of great 
length even up to the time of pairing. Moreover they stretch out in various planes, 
so that, although one may be safe in assuming that the threads are not all of the same 
length, this cannot be convincingly demonstrated. After pairing, however, and when 
the shortening and thickening of the bivalent structures has gone on for some time, 
the heteromorphic nature of the chromosomes becomes very evident. In figs. 20, 21, 
22, and 24, clear instances of long and short chromosomes are shown. This is even 
more striking in a polar view of the equatorial plate later on (fig. 33). As indicated 
in this figure, there are at least three distinct sizes of chromosomes. Of the fourteen 
bivalent chromosomes here shown, one is distinctly larger than the others, six are quite 
small, and the remainder are about half way between these two extremes in regard to 
their size. Perhaps the most significant feature in.this connection is the evidence 
which shows quite clearly that the chromosomes which conjugate with one another in 
the act of reduction are of the same length, that is, short ones unite with short ones 
and long ones with long ones. Instances of this are demonstrated in figs. 20, 21, 22, 
28, and 24. 
Another feature that appeared to be very constant, and one that has been noted by 
several other writers, is to be seen in fig. 24. When the bivalent chromosomes are 
completely organised, they distribute themselves at the extreme periphery of the 
duclear vacuole, the majority of them being in close touch with the nuclear 
membrane. 
* In an earlier investigation on this plant, the shorter chromosomes were mistaken for portions of the arms of the 
V-shaped structures. This led to an error in the count. 
