CHAPTER XIII 
MINUTE STRUCTURE OF LEAVES; FUNCTIONS OF 
LEAVES 
148. Leaf of Lily. — A good kind of leaf with which to 
begin the study of the microscopical structure of leaves 
in general is that of the lly. 
149. Cross-Section of Lily Leaf. — The student should first exam- 
ine with the microscope a cross-section of the leaf, that is, a very 
thin slice, taken at right angles to the upper and under surfaces and 
to the veins. This will show: 
(a) The upper epidermis of the leaf, a thin, nearly transparent 
membrane. 
(b) The intermediate tissues. 
(¢) The lower epidermis. 
Use a power of from 100 to 200 diameters. In order to ascertain 
the relations of the parts and to get their names, consult Fig. 93. 
Your section is by no means exactly like the figure ; sketch it. Label 
properly all the parts shown in your sketch. 
Are any differences noticeable between the upper and the lower 
epidermis? between the layers of cells immediately adjacent to 
each ? 
150. Under Surface of Lily Leaf. — Examine with a power of 200 
or more diameters the outer surface of a piece of epidermis from the 
lower side of the leaf.2 Sketch carefully. comparing your sketch 
with Fig. 94, B. and labeling it to agree with that figure. 
1 Any kind of lily will answer. 
2 The epidermis may be started with a sharp knife, then peeled off with 
small forceps, and mounted in water for microscopical examination. 
127 
