THE LIVING CELL ' 21 
When one of these is detached, mounted in water and 
examined under low power magnification, it is seen to be two 
layers of cells thick, except along the margin, where only one 
layer of cells is to be observed and in the central midrib region, 
where there occur several layers of narrow cylindrical cells. The 
CSS 
ye 
= a 
aw sae Cs ae Po Som esd o 
7 a kr 
XS 5 = 
_ wos Orga s sa — stevens Ve \ — am, 
— aE og, Ae AND | aig,” x ies es nik SN 
5 ey Se Te Cn ge oa SD ——- Pa 
as ab si IE SMEs abate. ey, 
eS SD IN 5 7229: 3S Si eat hte 
Sa “ie aie : ee — \ 
“— EEE, SJ 
an 
we 
BT HS Vea A Ba HUY 4 i 
ea ot RSS ) ay! 
LAAT ail HNN 
rt ‘ 
Fic. 12.—Portion of the leaf of Elodea, magnified. v, midrib; ¢, pointed cells pro- 
jecting at intervals from the margin. 
cells are arranged in rows and vary in size, being shorter and 
broader toward the midrib and longer and narrower near the 
margin. Projecting tooth-like cells occur along the margin. 
_ The cells of the upper surface appear about twice as broad as 
those of the lower surface. Each cell is separated from its 
neighbors by means of transparent ce// wails of cellulose and 
pectic substances. Just as in the onion epidermis, what appears 
to be a single partition wall between two cells is really two cell 
walls separated by a middle lamella. 
