MECHANICAL TISSUES 111 
the light yellowish wall is irregularly thickened, and the central 
cavity is very large. The pores are prominent. 
The stone cell of bitter root (Plate 32, Fig. 3) is nearly 
isodiametric. The walls are yellowish white and strongly por- 
ous and striated. The central cavity is about equal to the thick- 
ness of the walls. 
The stone cell of allspice (Plate 32, Fig. 4) is mostly rounded 
in form, and when the outer wall only is in focus it shows numer- 
ous round and elongated pores. The central cavity is filled 
with masses of reddish-brown tannin. The striations are very 
prominent. 
The diagnostic stone cell of aconite (Plate 32, Fig. 5) is 
rectangular or square in outline; the walls are yellowish and 
the central cavity has a diameter many times the thickness of 
the wall. The side and surface view of the pores is prominent, 
and the striations are very fine. 
POROUS AND NON-STRIATED STONE CELLS 
Porous and non-striated stone cells occur in Ceylon cinna- 
mon, in calumba root, in dogwood bark, in cubeb, and in echi- 
nacea root. 
The diagnostic stone cells of Ceylon cinnamon (Plate 33, 
Fig. 1) are nearly square in outline; the walls are strongly 
porous and the large central cavity frequently contains 
starch. 
The stone cells of calumba root (Plate 33, Fig. 2) vary in 
shape from rectangular to nearly square, and the walls are 
greenish yellow, unequally thickened, and strongly porous. 
The typical stone cells contain several prisms, usually four. 
The stone cells of dogwood bark (Plate 33, Fig. 3) have 
thick, white walls with simple and branched pores. The cen- 
tral cavity frequently branches and appears black when recently 
mounted, owing to the presence of air. 
The stone cells of cubeb (Plate 33, Fig. 4) are very small, 
mostly rounded in outline, with a great number of very fine 
simple pores which extend from the outer wall to the central 
cavity. The wall is yellow and very thick. 
The stone cells of echinacea root (Plate 33, Fig. 5) are very 
irregular in form; the walls are yellowish and porous, and the 
