PLANTING AND CARE OF TREES 



33 



The Root — According to their position, the roots of a tree 

 may be classified into tap-roots which grow directly down- 

 ward, surface or tracing roots which occupy a shallow layer just 

 below ground, and roots which take a position intermediate between 

 these two types. Some trees like the Hickory, the Bur Oak and 

 the White Oak regularly develop a strong deep-seated tap-root 

 and in consequence are able to draw water from the lower levels 

 but are difficult to transplant; others like the Birches and 

 Spruces have only surface roots and are therefore dependent 

 upon the supply of moisture in the shallow upper layers. Most 

 of our trees, like the Maple and Ash, are found to have a com- 

 bination of both kinds. Many fonns, moreover, in which one 

 of these two root types predominates are able to adapt themselves 

 to the condition of the soil in which they grow. Thus at the 

 Minnesota Experiment Station, a small Bur Oak growing on dry, 

 gravelly soil is reported to have developed a tap-root 20 feet long, 



Fig. 16. Seedling- of Hornbeam, after Strasburger. r zone of root- 

 hairs near root-tip; hw, main roots; sw, lateral roots; 1,1, foliage leaves; 

 e, seed-leaves. 



