CHAPTER XI 



MINUTE STRUCTURE OF LEAVES; FUNCTIONS OF 

 LEAVES 



159. 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 lily.-' 



160. 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 imder surfaces and 

 to the veins. This -will show : 



(a) The upper epidermis of the leaf, a thin, nearly transparent 

 membrane. 



(6) The intermediate tissues. 



(c) 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. 116. 

 Your section is by no means exactly like the figure ; sketch it. Label 

 properly all the parts shown in your sketch. 



Are any difEerences noticeable between the upper and the lower 

 epidermis? Between the layers of cells immediately adjacent to 

 each? 



161. 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. 117 and 118, and labeling it to agree with those figures. 



Examine another piece-from the upper surface ; sketch it. 

 How does the number of stomata in the two cases compare ? 



1 Any kind of lily wlU answer. 



^ The epidermis may be started with a sharp knife, then peeled off with 

 small forceps, and mounted in water for microscopical examination. 



150 



