ii 



STRUCTURE AND FUNCTIONS 15 



e c 



into substances suitable for the life and growth of the 

 plant. In the cross section of the leaf may also be seen 

 the cut ends of the fibro-vascular bundles 

 or veins. The surface of the leaves of many 

 plants are covered more or less profusely with 

 hairs (trichomes) (Fig. 3). 



The ROOTS, in the great majority of plants, 

 penetrate the soil and serve as holdfasts and 

 for the absorption of water and the various 

 salts which are contained in solution. How- 

 ever, they may also serve as aerial hold-fasts 

 for climbing plants, and in many cases for 

 storage of reserve materials. 



The typical root, or rather the type of 

 root (Figs. 4 and 5), which is 

 most common, consists of an 

 axial cylinder of cells sur- 

 rounded by a cortex, which in 

 turn is enclosed by the epider- 

 mal layer of cells. At the tip 

 of the root is a mass of dead 

 cells, which are in reality a part of the 

 epidermis. This mass is known as the 

 root cap, and serves to protect the more 

 delicate cells within. The epidermal 

 cells give rise . to a great number of 

 delicate hair -like structures which are 

 known as root hairs (Figs. 6, 7, and 8). 

 Each root hair consists of 

 very delicate living cells. 

 They ramify among the very 

 fine particles of soil, and ab- 

 sorb the moisture and the 

 salts which are in solution. FIG. 5. Cross sec - 

 > The water and the salts J of young 

 tion of young root. are transmitted from the 



a, axial cylinder ; c, , , , -, -, 



; roots through the stem to the leaves, 



FIG. 3. 



Trichomes 

 from leaf. 



cortex ; e, epidermis ; 

 p, root cap. 



to be used in connection with the 

 carbonic acid gas which is obtained from the air 



