826 
MR. W. GARDINER ON THE CONTINUITY OF THE 
blue in a 50 per cent, alcoholic saturated solution of picric acid, under the supposition 
that the latter might mechanically carry with it into the tissue the dissolved aniline 
dye, and that on washing out the picric acid with water, the protoplasmic threads 
would he left stained. Such treatment I found to be perfectly satisfactory, the 
threads running through the cell-walls and, indeed, the whole of the protoplasm being- 
stained blue, while the cell-wall either remained quite uncoloured or, if the action was 
forced, coloured but slightly, and to a much less extent than the protoplasmic threads 
which could still be easily recognised. 
As regards the action of picric acid, experiment seems to show that in addition to 
being one of the most valuable preservative media, it also restrains the coloration of 
the cell-wall by solutions of such a dye as Hofmann’s blue, which though a special 
stain for the protoplasm, will upon lengthy action stain the cell-wall also. Thus, if 
two sections be stained, one of alcohol material and the other of material which has 
been treated with picric acid previous to preservation in alcohol, in the former the cell- 
wall will be definitely stained, while in the latter little, if any, coloration will occur. 
Thus, the action of the picric acid is of twofold significance, not only serving as a 
vehicle for the passage of the Hofmann’s blue into the minute protoplasmic fila¬ 
ments, but also restraining at the same time the coloration of the cell-wall. 
It now only remains for me to describe in detail my method of manipulation with 
Chlor. Zinc Iod. and the picric acid solution of Hofmann’s blue. Sections of fresh 
material are cut in water and placed in ordinary iodine solution until they are 
well stained. They are then taken out by means of a platinum lifter, the iodine 
solution is removed with blotting paper, and they are mounted in Chlor. Zinc Iod. In 
those cases where the blue colour is not produced until after some time, it is usually 
possible to see something of any threads that may be present, and thus many very 
conclusive observations may be made prior to staining with picric-HoFMANN’s-blue. 
In fact, treatment with iodine will often bring out clearly many points that Hof¬ 
mann’s blue will not, such as a satisfactory demonstration of the passage of the threads 
through the substance of the middle lamella, where the lamella is well developed. 
Further, the threads appear thicker than with Hofmann’s blue, and in any case the 
treatment will give some idea of what one may expect to see after staining with the 
aniline dye. The time that Chlor. Zinc Iod. requires to act depends greatly upon the 
character of the tissue. With many dry endosperms and other cells with thickened 
walls it will take as long as twenty-four hours to thoroughly permeate the tissue. In my 
own experiments I was in the habit of mounting in Chlor. Zinc Iod. on one morning 
and staining on the following day. If not allowed to act for a sufficiently long time, 
it will be found that while some portions of the walls are swollen, others are hardly 
acted upon, and that the difference of refractive index of these two portions will give 
a very confusing appearance to the whole section, and very greatly hinder successful 
observation. Experiment alone can decide the time required for the conqffete action; 
