ROOTS 25 



25. Uses of roots. It was explained in Sects. 9 and 10 that 

 water is absorbed by roots and forced up into the stem of a 

 plant under considerable pressure. 



All plants must have water, at any rate during the part of 

 their lives when they are actively manufacturing plant food, and 

 it is by means of their roots that most familiar plants absorb 

 water and the substances that are dissolved in it. Yet absorp- 

 tion of water is not the only function of roots. They often ab- 

 sorb oxygen ; they commonly serve to anchor the plant ; they 

 may aid it to climb ; they frequently store food, water, or both ; 

 and in or on them there are sometimes carried on important 

 chemical operations which result in gaining material for the 

 production of plant food (Sect. 17). I\Iany kinds of roots repro- 

 duce the plant ; that is, a root or part of one may grow into a 

 new individual plant like the one to which the root belonged. 



The great importance of roots to life and growth is well 

 shown by the results which follow from any severe injury to 

 the root system. Cut off most of the roots of a tree and it 

 will die for lack of water. 



On the other hand, many (though not all) kinds of trees 

 may be cut down nearly level with the ground and still sur- 

 vive, the stump throwing up a vigorous crop of sprouts which 

 grow into saplings that eventually replace the fallen trunk. 



The necessity of roots for anchorage is well shown by Fig. 4. 

 In many cases the power of the roots to hold trees upright 

 is greatly increased by the formation of buttresses of wood, 

 which extend some distance up the trunk from the origins of 

 the larger roots (Figs. 259 and 260). In some great tropical 

 trees these buttresses attain enormous dimensions. 



26. Earth roots. The roots of most of the higher plants with 

 which we have practical dealings, such as forest trees and the 

 plants of the orchard, farm, and garden, are earth roots; that 

 is, they are formed, grow, and live at a moderate distance 

 under ground. Plants with roots suited to life in the earth 

 usually cannot grow as well in water as in soil, and they cannot 

 grow at all upon a bare rock, though sometimes they grow 



