ROOTS 



65 



The axis cylinder consists of the xylem and phloem, which 

 are arranged 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 cross-section. The 

 phloem lies between these projections. The tissues of which they 



Fio. 43. Seedling showing 

 soil held by root-hairs. 



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 surround- 

 ing the axis cylinder and probably corresponds to the starch 

 sheath of the stems. The cortex is a*broad zone of parenchyma 

 cells which frequently serve for storage of reserve food materials, 

 5 



