1906] MERRIMAN—NUCLEAR DIVISION IN ZYGNEMA 51 
then the chromatin bodies seen in jigs. 14 and 15 of Zygnema cells 
are homologous not with the chromosomes of Allium but with the 
granules seen in the earliest stage of the spirem, while groups in 
figs. 16 to 23 are directly comparable with the groups or rings of 
tetrads, which in Allium fused to form the tubular chromosomes. 
Zygnema possesses a mechanism of nuclear division less elabo- 
rated than that of the higher plants, inasmuch as dissociation of 
chromatin bodies occurs immediately after their association into 
primary groups without the intervention of a spirem. From this 
point of view appearances observed in Zygnema support the inter- 
pretation suggested in my account of nuclear division in Allium, 
namely, that the chromosomes are formed by fusion of bodies in 
groups, and that when a longitudinal splitting appears it is not to 
be considered a true splitting of a homogeneous substance but rather 
a dissociation of bodies which from the first were discrete. 
If this be true, then doubts may reasonably be entertained as to 
the validity of the conception held by Roux, and successively by 
many other investigators, that the complex apparatus for indirect 
division of the nucleus exists for the purpose of enabling each 
chromatin body to furnish its quota to the daughter nuclei. 
The essential feature of indirect division, and therein its advan- 
tage over direct division, appears to be the dissolution of the nuclear 
membrane. Thus is made possible a free interchange of nuclear 
and cytoplasmic substances and a renewal of the vitality of the cell. 
Zygnema, then, may be considered as furnishing additional evi- 
dence of interchangeability of nucleoli and chromatin bodies, of 
variability in their number, and negatively as furnishing no 
evidence that equal distribution of chromatin is effected by either 
transverse or longitudinal splitting of homogeneous bodies. Nuclear 
structures, cytoplasm, pyrenoids, and chromatophores are trans- 
ferred in equal amounts to the daughter nuclei and by a process 
differing not fundamentally in the result from that which would 
_ have been attained by direct division. 
NORTHFIELD, Mass. - 
