1140 Summers.—On the Occurrence of Lens-cells in the 
their edges the side walls are wedge-like, and as the angles of the wedges 
are 120°, where three walls meet they fit exactly. 
From angle to angle the diameter of an average cell is 72 ju, the side 
walls being 42 ju, in height (Fig. 4). 
In the middle the upper wall is slightly raised to form a papilla-like 
projection, the height here being 45 \i. The wall here is thinner but more 
strongly cutinized, so that after treatment with reagents a circular area is 
to be made out in surface view. Over this the deposit of calcium oxalate 
is almost absent, but towards the margin of the cell it increases in thickness. 
Over the middle of each side wall very little is deposited, however, so that 
there is a central clear area, with a surrounding almost opaque area, which 
*105 
X&2.5 
Fig. 3. Cells from the upper epidermis 
in surface view. 
F ig. 4. Cell from upper epidermis after 
removal of encrustation. 
is in turn bounded by a six-sided clear polygon. Darker radial lines connect 
the two brighter portions (Figs. 3 and 4). 
It has already been mentioned that the cells of the side epidermis over 
the assimilatory tissue possess much less calcium oxalate than those just 
described. A difference in shape also characterizes them (Fig. 5). The 
regularity in surface view of the first-mentioned cells is absent in the latter. 
In longitudinal section the side walls are seen to be thinner, while in the 
majority of cases the wedge-joints are absent. The basal wall is thinner and 
concave. From this basal wall the cell rises as a papilla-shaped structure, 
the average diameter being 25*5 /x, while the average height is 32 /x. The 
upper wall is pushed out slightly and a circular central refractive area is 
developed (Fig. 7). 
