HISTOLOGY 47 
Hustology of Leaves. 
Place a small piece of a lily leaf between pieces of 
pith and cut thin cross sections. (Pliable tissue like that 
in the blade of a beech or lily leaf can be cut much more 
E@tistactorily By folding it so as to have several 
thicknesses and then placing it between pieces of pith). 
Mount the sections in a little water, then add a drop of 
so per cent. glycerin. Study the sections under the low 
power until you know which is the upper and which is 
mie lower suriace. Find a thin place, where the cells 
appear definite and turn on the high power. A layer of 
light colored cells will be found both on the upper and the 
lower surface, called the upper and lower epidermis re- 
epectivery,  Elow amiany cells thick are each” of these 
overs’ \VVhat do the cells contain? Are the cell walls 
equally thick on the outside and the inside? Is this 
of any importance to the plant? Green colored cells will 
be found between the upper and the lower epidermis. 
Near the upper epidermis these cells will be found to be 
arranged in a more or less definite layer, the palisade 
parenchyma. What is the form of the cells in this layer? 
How many cells thick is it? Are there any spaces be- 
tween the cells? The cells between the palisade paren- 
chyma and the lower epidermis form a layer known as 
the spongy parenchyma. What is the relation in thick- 
ness between this layer and the patisade parenchyma? 
What is the form of the cells found in it? Compare the 
intercellular spaces with those found in the palisade par- 
enchyma, Compare the cells of the two layers men- 
tioned with regard to color. What is the green color due 
to? Masses of grayish colored cells will be found here 
