1901] THE MIDDLE LAMELLA tg 
quite deeply colored, the next is lighter, and the colors grow less 
and less intensé until the innermost layers show no coloration at 
all. After a ten minutes’ exposure to acid brown, sections were 
dehydrated, passed through clove oil, and mounted in Canada 
balsam, without affecting the staining, except that the color of 
the bast fibers was somewhat faded. The contents of the bast 
fibers are deeply colored by acid brown. 
The action of orseille (acidulated solution, twenty-four hours 
exposure) is exactly like that of acid brown. The effect of 
aniline-water-safranin, on the other hand, is similar to that of 
ruthenium red. 
Exposure to ponceau for various periods up to two and one 
half hours does not stain the bast. 
By treatment for a few minutes with methyl violet B, the 
middle lamella of the bast and all the other layers except that 
next the middle lamella are stained violet. 
It appears that in the bast, as generally elsewhere, the mid- 
dle lamella is of pectic nature; that the first of the secondary 
layers is nearly or quite free from pectic substances, and is com- 
posed of a mixture of cellulose and nitrogenous substances, and 
that the subsequent layers gradually increase in pectic content 
at the expense of the cellulose and nitrogenous constituents, 
until the last layer is perhaps again purely pectic. But, from 
the purplish-red color given by ruthenium red and the indiffer- 
ence shown toward methylene blue, it may be inferred that the 
pectic compounds found in these walls are not exactly the same 
as those common to the middle lamellae of other tissues. These 
inner layers, like the pectic lining of the canals in the xylem of 
Pinus, show that the ability of the cell to secrete pectic acid is 
not limited to a single period of its development. 
Acid alcohol sections treated for a few seconds with methyl- 
ene blue show a deep blue color in the middle lamella of the 
collenchyma walls, much deeper than in the remaining portions 
of the wall, which, however, are also somewhat stained. The 
boundary between the middle lamella and the next adjoining 
layers is not so sharply defined as in the xylem and bast. At 
