22 BOTANICAL GAZETTE (JULY 
showing a long-continued period of pectic deposition. In older 
fibers a middle lamella is deeply stained, the remaining layers 
very slightly or not at all. 
The bast fibers are stained throughout; no thickening layers 
are yet distinguishable. The middle lamella is already differen- 
tiated in the collenchyma, the other layers remaining uncolored. 
The middle lamella is especially deeply stained in the corners, 
and angular intercellular spaces are in some cases inclosed by it. 
Similar sections not treated with acid alcohol yield similar 
results. 
TILIA AMERICANA. 
Cross sections through rather young growing shoots were 
treated with acid alcohol and ruthenium red. 
_ The cambium walls stain deeply, in the youngest cells 
throughout their entire thickness. The radial walls are more 
deeply stained than the tangential, the corners especially deeply. 
Passing from the youngest cambium cells toward the bast or 
toward the xylem, the beginnings of the secondary thickening 
may be seen in a very thin unstained or only slightly stained 
layer of the wall within the stained portion. This is similar to 
the behavior of the cambium walls of pine, except that in Tilia, 
as generally, there is no evidence of a Zwischensubstanz, which, 
so far as I have observed, is found only in the pine cambium 
walls, The continuation of the deeply stained layer can be 
traced in the middle lamella of the much thickened xylem and 
bast elements. 
The middle lamella of the xylem stains deeply, especially at 
the angles, where it is enlarged. The rest of the wall is slightly 
tinged with red. 
The contents of the medullary ray cells are stained. Their 
walls are more uniformly stained than those of the xylem ele- 
ments, but the middle lamella is still plainly distinguishable. 
The bast has a deeply stained middle lamella, the other 
layers of the very much thickened wall being unstained or only 
slightly stained. In this respect, as in most others, the staining 
reactions of Tilia resemble those of pine. 
Pk 
