824 
MR. W. GARDINER ON THE CONTINUITY OF THE 
strong glycerine, the middle lamella may be made almost transparent; and when in 
such a condition will no longer present any hindrance to successful observation. 
But the better and more reliable reagent is Hofmann’s blue.'" As a result of 
numerous experiments I am able to state that this dye is a particularly satisfactory 
reagent for staining the protoplasm alone, and as such is of extreme value for botanical 
research, and supplies a long-felt want. I find that it works best after treatment with 
picric acid, and that unless the solution in alcohol be too strong or the staining be 
decidedly forced, there will be little if any coloration of structures other than proto¬ 
plasm. But when Hofmann’s blue is used, the washing-out of the sulphuric acid 
must be carefully attended to, for the two will not work together as in the case of 
Hofmann’s violet. After staining, the section is well washed with water and 
mounted in dilute glycerine. Such was the method I used in my investigation upon 
the structure of pulvini. Having thus dealt at some length with sulphuric acid, I 
must now proceed to describe in the same way Chlor. Zinc Iod. 
The action of this reagent is well known. It causes a swelling up of the cell-wall, 
and at the same time colours the cellulose blue. It is, however, much less violent in 
its action than sulphuric acid, causing but little distortion of form or displacement of 
relative arrangement. There is simply a slow and regulated swelling. Sections may 
be at once treated with Chlor. Zinc Iod., or may be first stained with iodine which 
helps as it were to accentuate its differentiating powers. The easy manipulation 
attending the use of Chlor. Zinc Iod., its high refractive index, and the satisfactory 
manner in which its gradual action may be observed, cause it to be one of the most 
valuable reagents employed in botanical research. For the demonstration of the 
presence of protoplasmic threads running through the thickness of the cell wall. 
TanglI first used Chlor. Zinc Iod. in his investigation upon the endosperm cells of 
Strychnos, Phoenix , and Areca The sections were first stained with iodine and then 
* Under the somewhat loose term aniline bine, are frequently included and described by writers a 
number of salts which are obviously perfectly distinct, both as regards chemical and physical characters. 
For example, there is soluble or water blue, insoluble blue, gentiana blue, phenylene blue, benzyl blue, 
methylene blue, cyanine or chinoline blue, Hofmann’s blue, besides others, Bavarian blue, Capri blue, &c., 
some of which are patented products of the various aniline-dye manufacturers. Frequently any given dye 
obtained from one maker will absolutely differ in staining properties from that of the same name obtained 
elsewhere. This being so, it is necessary to state very clearly the exact name and maker of any of the 
so-called aniline blues that may be made use of. I first used Hofmann’s blue at the Wurzburg labora¬ 
tory, and to the kindness of Professor Sachs I am indebted for the information that it is known as 
Hofmann’s blau (anilin blau), and may be obtained from Morelli, Druggist, &c., Semmel Strasse, 
Wurzburg. A tolerably strong solution is made in 50 per cent, alcohol, to which is added a drop or two 
of acetic acid. After staining, the section is washed with water and mounted in dilute glycerine or 
glycerine jelly. I find that when dyes are dissolved in solutions containing a higher percentage of 
alcohol than that named above, most dyes will lose their selective power for particular strucfures, and 
will begin to stain all tissues alike. These results are confirmed as regards animal tissues by Dr. Mayer, 
of the Naples Zoological Station. See Mt. Zool. Stat., Neapel ii. (1880), pp. 1-27. 
t Loc. cit. 
