Igor | THE MIDDLE LAMELLA 17 
either acid alcohol or fresh sections are deeply stained by ruthe- 
nium red throughout their whole thickness, but the cuticle 
remains unstained. This accords with Mangin’s results on 
cutinized membranes. 
NERIUM OLEANDER. 
Cross sections were cut through growing stems of various 
ages. The whole of the cambium wall is deeply and quite 
uniformly stained by ruthenium red either after or without previ- 
ous treatment with acid alcohol. Similar results are attained by 
a few seconds’ exposure to dilute methylene blue solution. The 
cambium walls are not stained by an exposure of three or four 
minutes to acid brown. The middle lamella of the xylem is 
deeply stained by methylene blue or ruthenium red, the other 
layers of the wall being colored very slightly if at all. The 
xylem walls are colored blue by methyl violet B. They are 
Stained quite uniformly brown in a few minutes by acid brown. 
They are stained uniformly red in forty-five minutes by aniline- 
water-safranin. After thirty minutes’ exposure to this safranin 
solution the xylem walls are colored bright red, the middle 
lamellae between the large tubes being decidedly darker than 
the thickening layers. After forty minutes’ exposure to ponceau, 
the thickening layers of the xylem are stained somewhat, though 
not evenly, the middle lamella remaining uncolored. 
Sections were exposed for twenty-four hours to neutral, 
acidulated, and alkaline solutions of orseille. The neutral and 
alkaline solutions produced the same coloration of the various 
tissues as the acidulated, but to a less degree. Therefore only 
the action of the acidulated solution will be described. The 
‘coloration of the xylem and medullary rays isa purplish-red, of 
all the other tissues affected, brown. The walls of the xylem 
have a general purplish tinge, but no distinctive staining is 
apparent in the different layers. The contents of the medullary 
ray cells are deeply colored, and the walls are stained similarly 
to those of the xylem. An exposure of two and one half hours 
to ponceau produces a reddish tinge in the xylem walls, and no 
further stain. 
