1901} THE MIDDLE LAMELLA 21 
throughout. The xylem shows a distinctive stain for the middle 
lamella, which is enlarged and especially deeply stained at the 
angles. The medullary ray walls and cell contents stain deeply. 
The middle lamella and successive thickening layers of the 
bast fibers stain exactly as described for Nerium, including the 
purplish tinge. The stain of the middle lamella is deepest at 
the angles. The lining layer of the canals running from fiber 
to fiber is deeply stained where it traverses unstained or less 
deeply stained layers. This recalls the deeply stained layer of 
the pits of pine tracheids, and, with the deep stain of the last 
- deposited wall layer in these tissues of the rose, shows these cells 
to possess the power very late in their history of depositing 
pectic wall material. 
The pith cells show a very distinctive stain for the middle 
lamella. 
In the collenchyma, the walls are stained throughout, the 
middle lamella much more deeply than the other layers, but the 
boundary between more and less deeply stained portions is not 
so clearly defined as in the xylem. The epidermal walls are 
Stained about the same as the collenchyma. The cuticle is 
unstained. 
Cross sections of a slightly older stem than that just 
described were stained with ruthenium red, then exposed for a 
few seconds to methylene blue. The xylem walls are stained 
purple by the combination, the middle lamella most deeply. 
The bast fibers take up both stains, the relative depth of stain 
of the various layers being about the same as with the red alone. 
The epidermal walls take up the blue more freely than the red. 
The collenchyma cells remain red. 
Cross sections of a very young growing shoot were treated 
with acid alcohol and stained with ruthenium red. The cambium 
walls stained deeply throughout. Very thin tangential red lines 
are visible, representing the earliest deposit of wall material. 
Such very thin tangential walls are what one would expect to 
find in material gathered in the season of active cambial growth. 
Young xylem elements have the walls entirely stained, 
