BOOTS AND THEIR RELATION TO PLANTS 25 



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 survive, 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 figure 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 for some distance up the trunk from the origins of the 

 larger roots. In some large tropical trees these buttresses 

 attain enormous dimensions. 



22. Earth roots ; direction and extent of root system. The 

 roots of most common flowering plants in temperate regions 

 are earth roots ; that is, they grow in and through the soil. 

 The nature of the soil greatly influences the extent and posi- 

 tion of the root system. Sandy soils favor the development 

 of an extensive root system, while clay soils do not. If the 

 good soil forms only a shallow layer over shale or sterile clay 

 (or in the arctic regions over ice), the roots spread out in a 

 flat, mat-like fashion. 



The smaller rootlets are so woven through the soil that it 

 is never possible to unravel the entire root system. The roots 

 of a single oat plant, if arranged in a straight line, have been 

 found to measure over 450 feet in length. Desert shrubs 

 sometimes send their roots down as much as 60 feet toward 

 the water supply. In parts of California it has been found 

 that common farm plants, such as alfalfa and wheat, may have 

 roots reaching moist earth at a depth of from 13 to 15 feet. 



Why is deep plowing between hills of half-grown corn 

 likely to injure the crop ? 



23. Pull of roots due to shortening. Frequently rootlets or 

 the taproots of herbaceous plants shorten after they are fully 

 grown. This shortening has a tendency to pull the stem and 

 leaves of the plant downward. It is interesting to notice how 

 some plants with rosettes of leaves, like chicory, dandelion, 



