STEUCTURE OF ROOTS 267 



the phellogen and the corky tissue outside of it. Draw. 

 The relation of bark to woody tissue in pine is shown in 

 Fig. 410. Cork tissue may be studied to advantage in 

 the skin of the potato. 



432. STRUCTURE OF ROOTS.— At the growing point 

 the root has a cap (of small compact cells) which 

 protects the delicate tissues from injury (Fig. 395). 

 Such a protection is not found in growing points (buds) 

 of stems. In their internal structure roots differ from 



410. White pine stem in radial longitudinal section. 



Traclieids on tlie left with medullary rays crossing them. Next to the wood 



is the phloem, then fundamental tissue, then the dark hark. 



especially when very young. Young roots have 

 the radial arrangement of phloem and xylem (427). The 

 number of xylem strands radiating from the center differs 

 with the plant. In roots also tljere is almost uniforml\ 

 present a true endodermis. This layer is found just 

 within the cortex and is composed of rather thick- 

 walled cells. However, many rhizomes and stems have 

 a trne endodermis. To sfiuh/ corn roots: From the roots 

 of Indian corn a few weeks old cut thin cross-sections; 

 stain and mount. With the aid of the low power make 

 a sketch showing the arrangement of the strands of 



