14 BOTANICAL GAZETTE [yuLy 
there can be no possible doubt of the number of chromosomes 
present. 
As already shown (fig. 20), one or in some cases more pairs of 
chromosomes may be cut off from the spirem before it undergoes 
segmentation, and frequently while it is still in the second contraction 
period. The exact method of origin of these pairs has not been 
observed, but they invariably, so far as observed, lie with their long 
axes parallel and connected at one end, from which it would appear 
that they were successive chromosomes on the spirem. In later 
stages, when the spirem has constricted into a chain of chromosomes 
arranged near the periphery of the nucleus, one or more pairs of 
chromosomes are found separated from the rest. Some of these have 
doubtless had the origin shown in fig. 20. Others appear to have 
originated later, as indicated in some of the figures, by successive 
chromosomes on the chain swinging around parallel to each other and 
thus pairing. Usually in diakinesis one or two such pairs are found, 
though occasionally there is no evidence of pairing. The highest 
number of pairs observed at this stage was five, with indications of 
pairing among the others (fig. 29); which is unusual. Later; in the 
multipolar spindle stage two distinct pairs are usually found in vary- 
ing stages of conjugation (jigs. 35, 36). A single case was observed 
(fig. 37) in which the fourteen chromosomes were all paired. 
As the figures indicate, constriction of the spirem at regular inter- 
vals proceeds progressively until a chain of chromosomes is formed. 
When this has taken place, the chromosomes are at first several 
times longer than broad, and their margins have a very irregular, 
sinuous outline, like that of the spirem just previous to segmentation. 
They are not so long, however, that they can be twisted and looped 
in the confusing manner of many heterotypic chromosomes of plants. 
This is very gratifying in the study of these stages, since it permits — 
a clearness of interpretation which would otherwise be unattainable. 
Figs. 22 and 23 show the beginning of contraction, which has pro- 
ceeded farther in fig. 24, leaving only the so-called linin connection 
between the chromosomes. The constrictions are all equivalent and 
the spirem thus segments into the sporophyte number of chromosomes 
and not into the reduced number of chromosome pairs. If successive 
chromosomes on the spirem are really the members of a pair, there is 
