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 lily.-' 



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 sho-w : 



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

 membrane. 



(b) The intermediate tissues. 



(c) The lo-wer epidermis- 

 Use a povrer 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 sho-wn in your sketch. 



Are any differences noticeable bet-ween the upper and the lo-wer 

 epidermis? bet-n'een 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 

 lo-ner side of the leaf.^ 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 

 staiall forceps, and mounted in water for microscopical examination. 



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