114 



BIOLOGY 



FIG. 56. CROSS SECTION OF 

 A MINUTE ROOT 



Showing the relation of the root hairs to 

 the cells of the root. 



the root. The root hairs are present in immense numbers 

 on the fine, delicate growing root tips, and grow in all direc- 

 tions into the soil. They are 

 thus brought into close contact 

 with particles of soil and serve 

 the plant as an organ for 

 absorbing water. All of the 

 nutrition that a plant derives 

 from the soil is drawn through 

 these root hairs, which are 

 closely connected with the 

 cells on the interior of the 

 root; so that liquids absorbed 

 by the hairs pass readily into 

 the substance of the root 



itself. From here they pass from cell to cell, and eventually 

 find their way to all parts of the plant. The root hairs, con- 

 stituting the absorbing organ of the plant, are of great func- 

 tional value. If a plant is forcibly pulled out of the soil, all of 

 the root hairs are torn from the root and left attached to the 

 particles of the earth. If, however, the whole plant is removed 

 from the ground and the soil is carefully washed from the roots, 

 the root hairs may be found still attached to the rootlets, and 

 may show grains of sand attached to the root hairs. 



STRUCTURE OF THE LEAF 



A complete leaf consists of three parts: The broadly ex- 

 panded blade; the contracted stem or petiole; and two little 

 appendages called stipules attached to the base of the petiole 

 where it is connected with the stem. The stipules are not 

 present in all leaves and are not found in the castor bean. 

 Running from the top of the petiole out into the blade are a 

 series of fine veins; in some plants they run in a parallel direc- 

 tion (parallebveined leaves), and in others they branch profusely 

 into many small twigs (netted-veined leaves). 



