ROOTS 



65 



The axis cylinder consists of the xylem and phloem,' which 

 are an-anged: radially and alternate. The xylem is in the center 

 of the root with branches that project outward towards the sur- 

 face, giving it a star-like appearance in crossrsection. The 

 phloem lies between these projections. The tissues of which they 



Fia. 43. — Seedling showing 

 ■ soil 'held by root-haira. 



Fig. 44. — Cross-section of rootlet showing root-hairs. 



are composed serve the same functions as in the stems. In the 

 older roots, a cambium is developed which gives rise to secondary 

 xylem and phloem as shown in the diagram. The endodermis 

 is a more or less definite sheath of starch-bearing cells surrouiid- 

 ing the axis cylinder and probably corresponds to the starch 

 sheath of the s.tems. The cortex is a broad zone of piarenchyma 

 cells which frequently serve for storage of reserve food materials, 

 5 



