1901] THE MIDDLE LAMELLA 23 
The walls of the parenchyma cells between the bast bundles 
show a stain throughout, the middle lamella appearing thin and 
deeply stained, and somewhat enlarged at the angles. 
In the collenchyma the whole wall and the cell contents 
are stained. Here, too, the middle lamella is thin and deeply 
stained, often including at the angles a less deeply stained 
area. 
The walls of the cork cells stain quite uniformly throughout, 
but not very deeply. The color is purplish, different from the 
bright red typical of the middle lamella in other tissues. No 
middle lamella is here distinguishable. If anything, the inner- 
most wall layer, next the lumen, is most deeply stainéd. Here, 
as in some of the tissues of Pteris, there is evidence that the 
middle lamella has undergone a chemical change, some or all of 
its pectic content having been replaced by other substances. 
The cuticle is unstained. 
ILEX OPACA. 
The tissues of the holly resemble those of the pine in their 
reactions to ruthenium red, the only stain I have used upon 
them. 
In cross sections, either with or without previous treatment 
with acid-alcohol, the cambium walls are stained throughout by 
ruthenium red, and their connection may be traced with the mid- 
dle lamellae of the xylem and bast. 
The middle lamella of the xylem is thickened at the corners 
and stains deeply; the rest of the wall stains but slightly. 
The middle lamella of the pith, which takes a deeper stain 
than the rest of the wall, is thickest at the angles, where it fre- 
quently encloses intercellular spaces. These spaces are some- 
times triangular or quadrangular, but usually with more or 
less rounded angles, and often of an elliptical or circular 
form, 
The middle lamella of the bast stains deeply, the rest of the 
wall slightly. The same is true in the collenchyma walls, where 
frequent angular intercellular spaces occur. The walls of the 
cork cells show no stain. 
