344 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
in the older literature are to be expected, for at the time, the steps in mitosis 
were not so specifically defined. In this description, reference is made to 
the individual chromosome and not to tetrads as such. 
My material was prepared by the modernized aceto-carmine method 
as described by Belling (19216). Material was also fixed in Flemming’s 
medium fluid followed by sectioning and staining. In addition to these 
methods, pollen mother cells were teased out on a slide into a 3 percent 
cane-sugar solution and studied in the living condition. The staminate 
hairs were suspended in 3 percent cane sugar, and the course of the divisions 
could be followed as described by Strasburger (Practicum, p. 604) for the 
staminate hairs of Tradescantia and by Lundegardh (19126) for root-tip 
divisions. The temperature was satisfactory when between 75 0 and 8o° F. 
The drawings of Plate XXIX were made entirely from aceto-carmine 
preparations. This is certainly a most valuable reagent for studying the 
chromatic elements of a cell to the exclusion of others. The solution may 
be employed in any dilution, and I found that for general purposes one 
drop of the modernized Schweigger-Seidel (1868) preparation added to one 
drop of water on a slide gave almost instantaneous staining. 
The fluid acts as a swelling agent, so that the preparations in a one-to- 
one dilution go to pieces in about a week. For this reason, it is desirable 
to know how soon after treatment the chromosomes will show any particu¬ 
lar stage in the swelling. 
The mother cells were teased from the anthers into a drop of water on 
a slide to which then was added, ordinarily, a drop of the aceto-carmine. 
The mount was made as described by Belling (19216), who first instructed 
me in the method. It was noted, in cases in which the stain was run under 
the cover glass, that about ten seconds were required to bring the chromo¬ 
somes into the sharpest definition. 
The structure came out with the first swelling, somewhat as does the 
image on a photographic plate, without any perceptible change either in 
the form or in the position of the elements from that seen in the living 
condition. The first perceptible change can be noticed in about an hour, 
when the elements may or may not appear a trifle swollen. When slight 
swelling occurs, it affords considerable advantage for studying the morpho¬ 
logical composition of the chromosomes. 
The figures given on the accompanying plates were, for the most part, 
made shortly after fixation, i.e., after some slight swelling had occurred. 
The effect with the reagent noted, while apparently altering the indices 
of refraction of the cell elements and thus increasing the sharpness of their 
differentiation, leaves the chromosomes, especially, quite unaltered except 
for the probable slight hydration. 
Most of the currently used killing agents, and especially the practice 
of hardening and imbedding, tend to greater density and even shrinkage 
of the cell structures. The use of such a fixative as this is especially advan¬ 
tageous as a check and for comparison. 
