1 6 Characteristics, Structure, Life of Trees 



itself in change of form of crown, or in lack of vigor. An 

 entirely different shape from the expected may develop. 



There are three types of root systems: the tap-root, the 

 heart-root, and the tracing-root; in some species the type 

 is and remains very pronounced, in others a change and 

 adaptation is more easily effected. 



The tap-root, perpendicular like the bole of a conifer and 

 penetrating deep into the ground, is adapted to deep soils, 

 and the difficulty of maintaining a hickory, a walnut, a fir, 

 or some of the pines in a soil which is shallow — due to 

 rocks or impenetrable layers, or groundwater close to the 

 surface — is often due to the inability of adaptation of their 

 tap-root systems. 



The oak, also a tap-root tree, adapts itself more readily 

 than those mentioned, splits up its tap-root into several strong 

 heart-roots, and develops a considerable quantity of surface 

 or tracing-roots, but then the short, stubby stature and rapid 

 tapering of the tree above ground shows that it is not in 

 its natural condition. Elm, ash, and linden behave in a 

 similar manner, hickory and walnut resent curtailment of 

 their tap-root more strenuously, and hence are difficult to 

 transplant or to grow on shallow soils. The spruce, on the 

 other hand, is one of the trees, which, with a typical tracing- 

 root system, developing horizontally in the upper soil strata, 

 can occupy the shallow soils without effect on its form devel- 

 opment. So can willows, poplars, and birches, while beech 

 and maple with a regular heart-root system made up of 

 several strong roots descending obliquely into the ground, 

 stand between the two types first mentioned, both in require- 

 ment for soil depth, and in adaptabifity. 



With the recognition of these characteristics in root 

 development we shall not expect the same species of trees 

 to produce the same form and remain alike under all 



