278 Reed . — The Nature of the Dotible Spireme in Allium Cepa. 
If any pairing of allelomorphs takes place at all it is obvious that the 
double type of spireme can hardly represent this phenomenon in A. Cepa , 
for the same type of spireme has been shown to exist in gametophytic cells 
where there can be no question of pairing of homologous chromosomes. 
It seems, rather, that this phenomenon is indicated by the pairs of chromo- 
somes of similar form which may be seen in the prophases, metaphases, and 
anaphases of somatic cells. During these three phases of nuclear division 
there is ample opportunity for any interaction between the members of 
chromosome pairs. 
In any case it now seems clear that in Allium Cepa ,as in Vicia Faba , the 
double type of spireme does not represent the paternal and maternal threads 
lying side by side. It does appear certain, however, as pointed out by 
Farmer and Digby (1 and 2 ), Farmer and Shove ( 3 ), and Fraser and 
Snell ( 5 ), that it merely represents the premature fission of the chromosomes, 
a fission which is generally effected at the anaphase or telophase of the 
division preceding that at which it will become operative. 
It has also been shown that in A. Cepa the longitudinal fission is 
recognizable at the anaphase of the preceding division and not the telophase 
as in Vicia Faba , and also that the fission is not effected by the pull of the 
lateral attachments between adjacent chromosomes, but that such lateral 
attachments merely accentuate a fission already formed within the chromo- 
some. It would be extremely interesting to know exactly what brings 
about the fission at this early stage. 
Further, the presence of a chromosome of a definite form — the hooked 
chromosome, # in PI. XVIII, Figs. 22, 23, and 24 — suggests that we may 
have here a feature of some special biological importance, but until it can be 
traced through all the nuclear phases of the plant it would be unwise to 
endow it with any particular function. 
Finally, it may again be remarked that the facts which have emerged 
from this investigation lend no support to Lawson’s recently propounded 
theories (10, 11, 12) to account for certain phenomena of mitosis. It has 
not been found possible to demonstrate in A. Cepa the presence of a nuclear 
membrane as a distinct entity, nor is it found that there is any sudden 
collapse of the nuclear vacuole which might call the spindle into being. 
It is quite true that Lawson’s results were mainly derived from the study 
of meiotic cells, but he maintains that the processes are the same in both 
meiotic and somatic cells. 
Summary. 
1. At the end of prophase chromosomes are arranged in eight pairs on 
the equatorial plate and the members of each pair roughly correspond with 
one another in form. 
2. The paired arrangement is preserved during the anaphases. During 
