4 PRINCIPLES OF AMERICAN FORESTRY. 



and Scarlet Oaks, which often have a tap-root extending 

 four feet in depth before the tree has attained a correspond- 

 ing height above ground, but after about five years large 

 lateral roots develop and the growth of the tap-root nearly 

 ceases. 



Root-growth is relatively less to the extent of ground 



FIG. 2. Characteristic Koot Formation. On the left two Hack- 

 berry, on the right two White Birch, each two-year seedlings from 

 same seed-bed; the first with a divided tap-root, the second 

 without tap-root. 



occupied in moist and fertile soil than in dry and poor soil, 

 but the roots are proportionately more branched. In wet 

 seasons the root development is less for a given plant than 

 in dry seasons, because the roots may get their needed 

 food and water from a small area. Nursery trees grown on 

 moist rich land have a more compact root system than 

 those grown on poor land. 



At the Minnesota Experiment Station a small Bur Oak 



