1 1 1 8 MichelL — On the Comparative A natowy of the 
off tubular thin-walled cork cells, and continues doing so until from fourteen 
to eighteen rows of cells have been formed. The cells which are now cut 
off have not the definite rectangular outline which characterizes the first 
type (PL XCVIII, Fig. 9) of cell formed, and they possess slightly thickened 
cellulose walls (PI. XCVIII, Fig. 10). These cells become more and more 
crushed and stretched as new cells are cut off from the cambium. It is not, 
however, till their outline is hardly recognizable that they become suberized. 
Text-fig. 4. P01 tulacaria afra. Diagrammatic representation of a section through the stem. 
P = pith ; xy. = xylem ; ph. = phloem ; C = cortex ; m.c. — mucilage cells, x 16. 
In the older parts of the stem it is these cork cells which constitute the bark, 
the first formed cork having worn away. In this no cell outlines are visible, 
and the lamellated appearance in section is due to the tangential walls of 
the original cells remaining distinct, while only traces of the radial walls are 
left. In C. gariepina the cork consists of a number of layers easily 
separated from one another, and in the young stem every alternate layer 
stains with safranin. Later on the cork stains uniformly, but the layers 
still remain distinct (PL XCVIII, Fig. 11). Possibly each of these layers 
represents the total amount of growth in one year. The fact that in 
