8o THE PLANT: A GENERAL INTERNAL VIEW 



Another tissue of the stele is the phloem. (See Figures 

 29 and jo.) Through the phloem the manufactured food 

 principally moves, having descended from the leaves. 



The advantage to roots in having the harder tissues in 

 the center rather than on the outside is evident. Think 

 of the way they must bend and burrow in the soil. But 



FIG. 29. Cross section of a young root showing root-hairs. The outermost layer 

 of cells is the epidermis. Note that the root-hairs are really prolongations out- 

 wards of certain cells of the epidermis. The thin-walled tissue of larger cells is 

 the cortex. The central region of smaller cells is the stele. The thick-walled 

 cells are xylem. The cells with shaded contents are phloem. 



with the stem it is different. In it the tissues of the stele 

 are differently arranged. Here rigidity is an advantage. 

 The leaves must be held firmly up in the light. The stem 

 must have strength to withstand winds. The pliability 

 of the root would be a disadvantage to the stem, unless it 

 is the stem of a creeping or climbing plant. Evidently it 

 is an advantage to most stems to have the tissue-arrange- 

 ment of the root reversed ; it is better to have the stronger 



