STRUCTURE AND FUNCTION OF ROOTS 



33 



FIG. 8. Cross section of rootlet in the region 

 of the root hairs. (From Stevens.) 



action which takes place between the contents of the root hairs 



and the soil water through the cell walls of the root hairs; these 



cell walls being admirably adapted to serve as osmotic 



membranes. 



70. Soil water holds 



various mineral salts in 



solution in small quanti- 



ties. These are absorbed 



with the water and 



furnish the mineral con- 



stituents of the ash. At 



the same time carbonic 



acid passes out from the 



root hairs into the soil and 



by its solvent action helps to break up the mineral constitu- 



ents of the soil, thus serving at once to disintegrate the rocks 



and also increase the quantity of 

 mineral salts contained in the soil water. 

 7 1 . The fluids absorbed by the root 

 hairs may then also be transferred 

 from cell to cell by osmotic action and 

 thus finally reach the tubular vessels 

 which lie near the axis of the root. 

 These vessels form a conducting tissue 

 through which the fluids may travel 

 freely, propelled by the osmotic force 



between the dotted lines is o f the thousands of root hairs on the 



shown on a larger scale in . , . , , 



the next figure. periphery of the root. 



FIG. 9. Diagram to show 



Structure and Function of the Stem 



72. The structure of the stem differs somewhat in its sig- 

 nificant features from that of the root. In a cross section of 

 a young stem we find, as in the root, a ground tissue of thin 



3 



