16 BOTANICAL GAZETTE [JULY 
The readiness with which the walls of the medullary rays take 
up methylene blue and ruthenium red, and also nigrosin, indi- 
cates the presence in them of both pectic and nitrogenous sub- 
stances. Their preference for ruthenium red indicates a greater 
proportion of pectic constituents than in the xylem walls. But 
against this view is the negative evidence of the ponceau, though 
this, perhaps, is not of much weight. 
The cells about the resin pits and their contents, if any, are 
always deeply stained by either methylene blue or ruthenium 
red. This indicates, according to Mangin, that the resin and 
other substances formed in the breaking down of these cells are 
wholly or chiefly decomposition products of pectic acid and its 
derivatives. 
The staining of the bast is in general similar to that of the 
xylem. In both acid alcohol and fresh sections, the whole wall 
takes up more or less freely either methylene blue or ruthenium 
red, the middle lamella being much more deeply stained than 
the inner layers. The middle lamella, of course, is thicker rela- 
tively to the total thickness of the wall, but is of about the same 
absolute thickness as in the xylem. 
The middle lamella of the collenchyma walls is generally 
stained more deeply than the other wall layers by methylene 
blue or ruthenium red, especially in sections treated with acid 
alcohol. Here, except at the corners, the unstained portion of 
the wall is very thin, and often the whole wall appears quite 
uniformly stained. The stain appears more diffuse than in the 
xylem, and the distinction between the more and less deeply 
stained layers is not so sharp. The middle lamella is enlarged 
at the angles of the cells, and sometimes encloses a triangular 
or quadrangular intercellular space. 
The appearance of the collenchyma is very much the same 
in longitudinal as in cross sections. The collenchyma walls 
become red when treated for thirty minutes with acidulated 
orseille solution, indicating the presence of some cellulose, but 
no distinctive stain for different portions of the wall is observable. 
The walls, except the outer ones, of the epidermal cells in 
