271 
Seedlings of Zea Mais and Phoenix dactylifera . 
embedding. An interpretation of the effects produced awaits an extension 
of our knowledge of the chemical and physical reactions between proto- 
plasm and the various reagents used in micro-technique. 
In order to obviate as far as possible particular effects due to chemical 
or physical action of the killing fluids, a number of different fluids were 
used and different stains employed after each method of fixing. The 
technique was rather difficult on account of the delicacy of the material. 
The following results were observed with the respective killing fluids. 
Saturated Solution of Picric Acid in 50 per cent. Alcohol. The mate- 
rial prepared for study by this reagent was unsatisfactory. The proto- 
plasmic structures were not fixed well enough to show with any definiteness. 
On the other hand, this is a good reagent for fixing the proteid granules. 
(Zimmermann, ’ 93 , p. 216.) 
Aqueous Picro-corrosive Fluid. I used the following modification of 
Mann’s method as given by Huie (’ 97 ). One volume of a saturated 
aqueous solution of mercuric bichloride was added to three volumes of 
a saturated aqueous solution of picric acid. The material was allowed to 
lie in this fluid for twelve to eighteen hours, then washed in water and 
dehydrated in the usual way with alcohol. This proved to be a very satis- 
factory killing fluid. The amount of picric acid present was sufficient to 
fix perfectly the granules, while the mercuric bichloride hardened the 
protoplasm and precipitated the soluble proteids. In a few cases there 
was a tendency to contract the cell-contents in the scutellum of Zea. 
Kleinenherg s Picro-sulphuric Acid. The results obtained by the use of 
this reagent indicated that it was better than picric acid alone, but not 
so good as the picro-corrosive fluid. The material seems to be insuffi- 
ciently hardened. 
Chromo-Osmo- Acetic Acid. Mottier’s formula, Pring. Jahrb. Bd. 30, 
p. 170. This fluid is a good fixing agent for the protoplasmic structures of 
the cell, but not for the granular structures. It produced no shrinking in 
any of the cases where it was used. 
Iridium chloride in Acetic Acid. The formula used was — 
Iridium chloride 1 per cent, aqueous solution . . 25 cc. 
Glacial acetic acid . . . . . . . 75 cc. 
It leaves the tissue in better condition for the stain than the following 
killing fluid, but in other respects the two act similarly. 
Worcester’s Killing Fluid. This fluid gave uniformly good results when- 
ever used. The formula according to which it is made is as follows : — 
Mercuric bichloride, saturated aqueous solution . 9 6 parts. 
Formalin (40 per cent, formaldehyde) . . 4 „ 
Acetic acid, 10 per cent. 10 „ 
Formic acid, to each litre of solution 5 drops. 
