Igor} THE MIDDLE LAMELLA 9 
In general, sections after staining were mounted in water and 
studied immediately. Ruthenium red preparations can be dehy- 
drated by absolute alcohol, passed through clove oil, and mounted 
in Canada balsam without affecting the stain. But the color 
gradually fades out from sections so treated, some tissues, notably 
the xylem and bast, losing their color almost entirely within a 
few weeks, while others, as the parenchyma and pith, retain it 
much longer. Sections stained with ruthenium red and mounted 
in glycerin jelly lose their color almost entirely in the course of 
a few hours. 
Mangin (4, 6, 7, 8) has classified the coloring matters used 
in staining plant tissues, and has described their reactions upon 
the various substances found in cell walls. Of the great num- 
ber of stains named by him, the following were employed in this 
investigation: | 
Orseille, which colors cellulose in neutral or slightly acidu- 
lated solution, but does not affect callose. 
Aniline-water-safranin (phenosafranin), methylene blue, Bis- 
marck brown (Vesuvian brown), fuchsin, and methyl violet B 
(violet de Paris), which do not color callose or cellulose, but do 
color pectic acid in neutral or acidulated solution. They also 
color equally well nitrogenous substances (lignin, cutin, etc.), 
but these may be distinguished by their retention of the color 
after treatment with alcohol, glycerin, or acids, which treatment 
decolorizes pectic acid. According to Strasburger (11), safranin 
colors the protoplasmic contents of the cell, the lignified wall, 
cork, and cutinized membranes cherry-red, the pectic substances 
Orange-yellow. Methylene blue colors the protoplasmic con- 
tents and lignified walls blue, the pectic substances violet-blue. 
Acid brown, nigrosin, and ponceau, which do not color pec- 
tic compounds, but strongly color nitrogenous substances. By 
mixing one of this series with one of the preceding, Mangin 
obtained distinctive double stains. 
Ruthenium red, which Mangin found the most satisfactory 
distinctive stain for pectic compounds. It differs from the other 
pectic stains, as safranin and methylene blue, by the fact that 
