476 THE BEAN PLANT. [CHAP. 



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 guard- 

 cells bounding each stoma. 



e. 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 | objective : they 

 will be found to consist of partially unrolled spiral 

 vessels. 



c. The flower. 



1 . 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. 



(3. Inside the calyx the corolla: the most con- 

 spicuous part of the flower, 

 y. Inside the corolla the stamens. 

 8. Within the stamens the pistil. 



2 . The calyx. 



A cup terminated at its free edge by five prominent 

 points, two dorsal, and three ventral : the five small 

 midribs running along it (one to the end of each of 

 the points) represent the free ends of five sepals, 

 which are united below. 



3. The corolla. 



a. Composed of five pieces or petals. 



a. On the dorsal side, a single large piece (vexil- 



