34 PLANT BIOLOGY 



The extent of root surface is usually very large, for the 

 feeding roots are fine and very numerous. An ordinary- 

 plant of Indian corn may have a total length of root 

 (measured as if the roots were placed end to end) of several 

 hundred feet. 



The fine feeding roots are most abundant in the richest 

 part of the soil. They are attracted by the food materials. 

 Roots often will completely surround a bone or other 

 morsel. When roots of trees are exposed, observe that 

 most of them are horizontal and lie near the top of the 

 ground. Some roots, as of willows, extend far in search 

 of water. They often run into wells and drains, and into 

 the margins of creeks and ponds. Grow plants in a long 

 narrow box, in one end of which the soil is kept very dry 

 and in the other moist : observe where the roots grow. 



Buttresses. With the increase m diameter, the upper 

 roots often protrude above the ground and become bracing 

 buttresses. These buttresses are usually largest in trees 



which always have been 

 exposed to strong winds 

 (Fig. 35). Because of 

 growth and thickening, 

 the roots elevate part of 

 their diameter, and the 

 washing away of the soil 

 makes them to appear as 

 FIG. 35. THE BRACING BASE OF A if having risen out of 



F,ELDP,NE. the ground 



Lerial Roots. Although roots usually grow underground, 

 there are some that naturally grow above ground. These 

 usually occur on climbing plants, the roots becoming sup- 

 ports or fulfilling the office of tendrils. These aerial roots 

 usually turn away from the light, and therefore enter the 



