20 ANATOMY AND PHYSIOLOGY 



11. Give one explanation of the difference in the rate 

 of transpiration from the two surfaces of the leaf. 

 Is this the only explanation? 



CROSS-SECTIONAL VIEW 



12. Mount thin free-hand sections of a fresh leaf show- 

 ing the internal anatomy as seen in cross-section. 



13. Identify in your section the two epidermal layers. 

 How many cells thick are they? Do you find 

 any chloroplasts in these layers? 



14. Are all the epidermal cell- walls of the same thick- 

 ness? Describe any variations observed. 



15. Is there a thick, continuous pellicle over the surface 

 of the leaf? Is it composed of cells? Such a 

 pellicle, when it occurs, is called cuticle, and is com- 

 posed of a waxy material, cutin. 



1 6. Compare the thickness of the cell- walls in the upper 

 and the lower epidermis. 



17. Note the stomata and guard-cells, and their relation 

 to the other epidermal cells. 



18. The tissue between the two epidermal layers is 

 composed chiefly of leaf-parenchyma, or mesophyll, 

 in which are imbedded the veins. Mesophyll, and 

 all other tissue containing chlorophyll, whether 

 found in leaves or in other organs, is also called 

 chlorenchyma. Note that the mesophyll is com- 

 posed of two distinct groups of cells, as follows: 



19. The more compactly lying cells beneath the upper 

 epidermis compose the palisade layer, or palisade 

 parenchyma. Describe their shape, contents, rela- 

 tive size, and relation to each other and to the 

 epidermis. 



20. Between this layer and the lower epidermis lies the 



