CHAPTER XII. 
Minute Structure of Leaves; Functions of Leaves. 
‘133. 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. 
134. Cross-Section of Lily Leaf. —'The student should first examine 
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 evidently show : 
(a) The upper epidermis of the leaf. 
(6) The intermediate tissues. 
(c) The lower epidermis. 
Use a power of from 100 to 200 diameters. In order to make out the 
relations of the parts, and to get their names, consult Fig. 96. Your 
section is by no means exactly like the figure. 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 ? 
The teacher can (after considerable practice) prepare such sections by 
doubling the leaf crosswise once or twice, and then slicing the required 
sections from the end of the folded leaf, held firmly in the hand, if 
necessary between bits of elder-pith to hold it in position. The razor 
must be sharp, and the stroke made rather quickly and long.2 The 
upper edge of a section may be distinguished from the under one by the 
presence in the former of palisade cells, so called from their resemblance 
to the high fence known as a palisade, made of stout stakes driven into 
the ground, Fig. 96. Mount in glycerine for temporary use in class. 
135. 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. Sketch carefully, comparing your sketch with Figs. 97 
and 98, and labeling it to agree with those figures. 
* 1 Any kind of lily will answer. 
2 Consult Clark’s Practical Methods in Microscopy, pp. 67-70. 
3 The epidermis may be started with a sharp knife, then peeled off with small 
forceps, and mounted in water for microscopical examination. 
