Reed . — - The Nature of the Double Spireme in Allium Cepa. 273 
development of the spireme, for when the latter is complete they have dis- 
appeared, and, as was shown above (Fig. 16), the nucleolar core is left as 
a faintly staining body within the cytoplasm (PL XVIII, Fig. 16). 
These bodies may simply represent waste material produced by the 
nucleus during the 'resting 5 stages, which material might then diffuse into 
the cytoplasm during the early stages of mitosis, or represent some substance 
which is used in the process of organization of the spireme. 
No useful purpose would be served here by detailing the various views 
which have been held as to the possible function of the nucleolus. It seems 
quite certain that it is a storehouse of reserve material which is used up in 
the formation of chromatin, but this may be only one of its functions. 
From the early stages of its formation the spireme is seen to be 
a double structure. At first it consists of a double series of irregularly 
shaped granules lying side by side in the nuclear framework (PI. XVIII, 
Figs. 3 and 4). Gregoire ( 7 ) has described this structure for several species 
of Allium , and has pointed out that the doubling is brought about by 
an alveolization of the chromatin band. Lundigard ( 14 ) also describes 
the split spireme for Allium. These observations also bear out Gregoire’s ( 7 ) 
statement that the spireme is not built up of chromatin discs on a linin 
framework. No evidence is found to support the observations of Merri- 
man ( 15 ) that the thread is a quadripartite structure. 
The separation of the spireme into two parallel longitudinal bands is 
regarded as a definite fission, and, as will subsequently be shown, the split 
first makes its appearance in the anaphases of the preceding divisions, and 
not at the metaphase of the same division, as described by Schaffner ( 20 ), 
or the prophase, as stated by Gregoire ( 7 ), who says ' the longitudinal 
division is essentially a prophase phenomenon ’. 
The more or less isolated granules of the early spireme spread them- 
selves over the nuclear groundwork and form a fairly homogeneous ribbon 
(PI. XVIII, Figs. 6, 7, and 8). It is at this stage that the spireme becomes 
segmented. At first it appears to break up into a number of lengths. The 
number is, in all probability, eight, and each segment is a long, often twisted, 
double band. These segments are usually bent somewhere near their 
middle, and it is common to find the parts on either side of the bend with 
similar configurations (PI. XVIII, Figs. 9, 10, 11, 12, and 13). Later these 
subdivisions break across transversely, and the sixteen chromosomes which 
characterize the somatic cells appear (PL XVIII, Figs. 14, 15, 1 6, and 17). 
In other words, there appears to be a preparation at this stage for the paired 
arrangement of the chromosomes, which will be described presently. 
A short digression must be made here to describe other changes which 
have been taking place in the nucleus during the prophases. 
The 'resting 5 nucleus occupies about half the cell volume (PL XVIII, 
Fig. 1) ; the organization of the spireme involves a very considerable increase 
