34§ 
AMERICAN JOURNAL OB' BOTANY 
[Vol. io, 
This photograph was taken from a stamen hair suspended in 3 percent 
cane-sugar solution and unstained. The chromosomes are living, and 
numerous ones appear quite smooth. It was found that the greater the 
density of the sugar solution, the greater was the apparent smoothness of 
the chromosome outlines. 
The central axis of the chromosome remains clear of these bodies. One 
may say that its structure, in this sense, is tubular. To use a homely 
comparison, if one could fill a sausage skin with irregular pebbles in such 
a manner that the central axis would remain clear, and if the pebbles 
pressed against the skin so as to give it an irregular nodular outline, this 
would represent crudely the structure of the chromosome. The bounding 
membrane would, of course, represent merely the linin surface, and a truer 
description would perhaps regard the chromomeres as more or less imbedded 
in a linin cylinder as a continuous phase. Figure 19, Plate XXX, also 
from a living unstained preparation, shows, in the upper half, the ends 
of two chromosomes. In these two, the hollow structure is quite obvious 
even in the photograph. It was, naturally, much more so to the eye of 
the observer. 
An outer chromosomal membrane such as Wenrich (1916) describes 
for Phrynottetix has never been observed by me in Tradescantia. Such 
a membrane could be demonstrated neither in the living chromosome in 
a sugar solution nor in any of the fixed material. For the present, I prefer 
to consider such figures as Lee’s figure 4, Plate I, (1920) to be due to the 
action of fixing fluid which caused the chromatin to shrink, thereby leaving 
the achromatic substratum through which it was originally distributed 
unchanged in form. His vacuolated condition of the plant chromosome 
as distinguished from the solid structure of the animal chromosome must 
also be due to the fickleness of our preparation methods. 
In figure 9, Plate XXIX, the chromosomes are about to be oriented 
on the equatorial plate. One observes here several whose longitudinal 
axes lie parallel with the optical axis of the microscope so that the ends 
are presented to the eye of the observer (b, fig. 9). 
The relationship of the chromomeres, one to the other, is somewhat 
variable. Sometimes they show traces of a spiral arrangement (figs. 17, 
18, PI. XXX). At other times they are mostly paired, as in figure 16, 
or else irregularly spaced as in figures 11 and 13, Plate XXIX. In figure 
12, chromomeres 2 and 3, 5 and 7, 10 and 12, 13 and 14, are located in the 
median optical plane of the chromosome and possibly opposite each other, 
so that the free spaces taken along the chromosomal axis represent the 
distances between them. The chromomeres 4, 6, 8, 11, and 15 of this 
figure overlie the hollow center and more or less overlie the other chromo¬ 
meres. 
This figure represents a chromosome that became freed from its mother 
cell. Part of the cell wall had been torn by the needle while being teased 
