viri.] THE BEAN-PLAXT. 83 



S. The epidermic layer of the lower surface ; 

 like a. 



c. The intercellular spaces, through the whole 

 thickness of the leaf: the direct communica- 

 tion 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./. 

 Draw. 



c. Treat with iodine : make out the sac, proto- 

 plasm (primordial utricle), nucleus and vacuole 

 of the cells : the starch granules. 



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

 examine with a low power : note 



a. The large close-fitting cells, with irregularly 

 wavy margins and no chlorophyll, which 

 chiefly make up the epidermis. 



/?. The openings here and there in it (stomata} ; 

 the two curved, chlorophyll-containing cells 

 bounding each stomate. 



f. Gently pull a midrib in two across its long 

 axis note the fine threads uniting the two 

 broken ends ; cut them off with a sharp pair of 

 scissors, mount in water and examine with 

 or -J objective : they will be found to consist 

 of partially unrolled spiral vessels. 



e. The flower. 



i . Its general structure. 



a. Borne on a short stalk (peduncle}. 



b. Composed of four rows or whorls of organs, 

 a. The external green cup-like calyx. 



