56 LABORATORY AND FIELD EXERCISES 



the relative thickness of the cell walls as well as 

 the size aud the living contents of the guard cells. 



c. Mesophyll. 



(1) Note the character of a mesophyll cell as regards 

 cell wall and cell contents. Does each meso- 

 phyll cell come in contact with an intercellular 

 space ? What would be the advantage of such 

 an arrangement ? What is your conception of 

 the intercellular system of a leaf ? Is it a con- 

 tinuous aerating system or are the spaces seen 

 in a transverse section isolated spaces ? Do you 

 find any intercellular spaces immediately above 

 the stomata? 



d. Veins. Study the structure of the veins. By what 



kind of tissue are the ducts surrounded ? Is there 

 a phloem like that connected with the xylem of 

 stems ? What is the double function of the veins in 

 a leaf ? 



e. The skeletal tissue. Study its distribution and the char- 



acter of its cells. 



/. Drawing. Construct an accurate drawing of a small 

 portion of your section so as to include a large vein. 

 Detail the tissues of the epidermis, mesophyll, veins, 

 and skeletal structures. 



