July, 1923] 
SANDS — STRUCTURE OF CHROMOSOMES 
349 
from the anther sac, but when the cell was found the metaphase-plate 
figure was still in position and intact. By pressing successively on the 
cover glass with a fine, springy needle, the chromosomes were finally sepa¬ 
rated from' the cytoplasm. By proper manipulations, often by merely 
tapping the microscope stage with a pencil, the specimens would roll over, 
thus permitting the observer to view all sides of the chromosomes. The 
chromosome in question was studied in this way, and it was then discovered 
that the chromomeres numbered 4, 6, 8, 11, and 15 were opposite others 
separated from them by the hollow center of the chromosome. The whole 
chromosome was found thus to have a rather regular four-rowed construc¬ 
tion. (See Nawaschin, 1911.) That this is perhaps not a general condi¬ 
tion is shown by the arrangement in figure 1, Plate XXIX, where chromo¬ 
meres 4, 7, 8, and 20 seemed to be arranged in various positions with res¬ 
pect to the others. Here, again, the arrangement of those in the median 
optical plane of the chromosome appeared opposite. 
In figure 2, the chromomeres have been numbered with reference to 
their distance from the eye-piece as determined by focusing up and down 
through the mass of the chromosome. Chromomere no. 1 is nearest to the 
eye; no. 14, the farthest from the eye. Those between are in successively 
intermediate positions. 
It is considered that in figure 12, chromomere 16 is at the distal 1 end 
of the chromosome, i.e., at the end away from the spindle attachment. 
Chromomeres 2, 5, 8, and 10 are therefore higher than 3, 7, 9, and 12. In 
the same figure, chromomeres 4, 6, 8, and 11 seem to have the planes of 
their sides somewhat oblique to the long axis of the chromosome. The 
arrangement as a whole simulates a segmented spiral, which is also the 
case in figure 5, notably, here, between chromomeres 10, 11, 12, and 13. 
On the other hand, one arguing for the view that the chromomeres are 
parts of fragmented disks and hence opposite will find, as noted, some evi¬ 
dence to support such a claim. 
An understanding of the true construction of the chromosome is ob¬ 
viously very dependent upon a study of the segments in all possible optical 
planes. Let text figure 2 represent the cross section of a chromosome when 
the construction is assumed to consist of four rows of chromomeres arranged 
opposite to one another, and the line po the median optical plane. If the 
focus is adjusted to the line xy, the image of the chromosome will show 
numerous, practically solid, cross striations or bands. It was by care¬ 
fully focusing up and down that chromomere c, figure 9, Plate XXIX, and 
the overlying chromomeres in figure 1 of the same plate were located. In 
the latter case, the specimen was rotated on the microscope stage by tap¬ 
ping, and its cross section while on end was studied. The band-like struc¬ 
ture is seen here and there in figure 10, Plate XXIX, while in figure 9 the 
two-ranked chromomeres, as well as a band in a few cases, are seen, accord- 
1 Wenrich (1916). 
