THE SPERMAPHYTES. 



211 



off a thin slice of the epidermis, mount in water, and ex- 

 amine the stomata under high power. Run the finger 

 over the edges of the leaves. What is noted ? Cut cross 

 sections of the leaves of different species. What is the 

 shape of the cross section in each case ? Examine with a 

 magnifying glass and draw, showing all you see. Measure 

 or estimate the greatest diameter of the leaves. 



Study Fig. 134, which is a picture of a thin cross section 

 of the leaf of the Red Pine, Pinus resinosa, or Norway 

 Pine. Around the out- 

 side is a single layer of 

 cells with thick walls, A, 

 the epidermis. This cov- 

 ering of thickened tissue 

 protects the softer in- 

 terior of the leaf. At the 

 corners, B and B, are 

 large cells whose irregu- 

 larity causes the rough- 

 ness of the edges. Just 

 within the epidermis is 

 another narrow band of 

 thick-walled cells, the 

 hypoderma, O. Within this is a broad band of delicate 

 parenchyma with folded cell walls, D. This is the 

 mesophyll. When the leaf was living these cells were 

 filled with protoplasm bearing green chlorophyl bodies. 

 Situated in the mesophyll are five large resin ducts, E, 

 each surrounded by a row of glandular cells which 

 secreted the resin. Next within is an elliptical ring of 

 oval cells, F, the endodermis, or bundle sheath. The 

 bundle sheath incloses thin-walled parenchyma, 6r, which 

 did not contain chlorophyl, and two fibrovascular bundles. 

 Each fibrovascular bundle consists of two parts. The 

 woody part or xylem is situated towards the flat or upper 



FIG. 134. Leaf of Red Pine, Pinus resi- 

 nosa. Transverse section. A, epi- 

 dermis; B, B, enlarged corner cells; 

 C, hypoderma ; D, mesophyll ; E, resin 

 ducts ; F, bundle sheath ; G, colorless 

 parenchyma. 



