XVI.] THE BEAN PLANT. 475 



perpendicular to its surfaces. Let the section lie 

 in alcohol * a few minutes to drive the air out of its 

 intercellular spaces, and then mount it in water, 

 and examine with i inch objective. 



b. Begin at the upper surface (marked out by its 

 more closely packed cells), and work through to 

 the lower. Note 



a. The colourless epidermal layer consisting of a 

 single row of cells ; the openings here and there 

 in it (stomata). 



ft. Beneath the upper epidermis come elongated 

 chlorophyll-containing cells, set on perpendicu- 

 larly to the surface, forming the palisade paren- 

 chyma. 



y. Then come irregularly branched cells forming 

 the lower half of the leaf-substance ; these also 

 contain chlorophyll. They constitute the spongy 

 parenchyma. 



8. The epidermal layer of the lower surface ; like a. 



f. The intercellular spaces, through the whole thick- 

 ness of the leaf: the direct communication of 

 some of them with stomata. 



. Here and there sections of ribs or veins : make 



out in them the same elements as in c. 2. c. 

 Draw. 



c. Treat with iodine : make out the wall, protoplasm 

 (primordial utricle), nucleus and vacuole of the 

 cells : the chlorophyll grains, the starch granules. 



d. Peel off a strip of epidermis from a leaf and ex- 

 amine with a low power : note 



1 This will extract the colouring matter from the chlorophyll grains. 



