viii.] THE BEAN-PLANT 79 



b. The root. 



a. Its main central portion (axis). 



b. The irregularly arranged rootlets attached to the 

 axis. 



c. The absence of chlorophyll in the root. 



d. The root-sheath, covering the tip of each rootlet: 

 this is difficult to get whole out of the ground in 

 the bean, but is readily seen by examining the 

 roots of duckweed (Lemna) with i inch obj. In 

 the latter plant it consists of several layers of 

 cells forming a cap on the end of the root, and 

 ending abruptly with a prominent rim some way 

 up it. 



c. The stem. 



1 . Erect, green, four-cornered, with a ridge at each angle ; 

 not woody; the gradual shortening of the internodes 

 towards its apex. 



2. Cut a thin transverse section of the stem through an 

 internode; note its central cavity, and the whitish ring 

 bi fibre-vascular bundles in it, which is harder to 

 cut than the rest : mount in water and examine with 

 i inch obj.': note 



a. The medullary or pith-cavity in the centre of the 

 section. 



b. The pith-cells, around the central cavity : large 

 and more or less rounded (parenchyma) : some- 

 times with dotted walls from spots of local thin- 

 ness on them. 



c. The epidermis: composed of a single layer of 

 somewhat squarish-looking cells, containing no 

 chlorophyll. 



