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 stria tions 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. i) 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 



