RESULTS OF MEASUREMENTS. 



35 



doubtless magnified by the effects of competition, since the roots 

 were necessarily one-sided. The importance of this is shown later. 



CONDITIONS THAT INFLUENCE ROOT EXTENT. 



While each tree species has a distinct root form tap or lateral 

 each shows more or less adaptability to the moisture conditions under 

 which growth is made. Lack of moisture induces long roots. Hence, 

 to compare cottonwood, which is invariably planted on moist situa- 

 tions, with osage orange, which is commonly found on the drier ones, 

 is not quite fair to the latter. A careful study of the original data 

 on which Table 4 is based indicates that there are a number of con- 

 ditions which reduce the amount of moisture available for the trees 

 and hence stimulate root growth into the good soil of fields, where it is 

 undesirable. The causes of extensive roots are as follows: 



(1) Lack of rainfall. Where the rainfall is light the roots will go 

 far in search of moisture. 



(2) Light and infertile soils. 



(3) An impermeable subsoil. Stiff clays and gumbo can not be 

 penetrated by the roots, nor do they permit moisture from lower 

 strata to reach the roots. 



(4) Lack of capillary water. This is greatest when the water 

 table is very low. 



(5) A heavy soil cover of grass or other deep-rooted plants. Cul- 

 tivation in the root zone conserves the moisture and hence reduces 

 the necessity for long roots. The effect of cultivation on the root 

 extent of osage orange is clearly shown by Table 5. 



TABLE 5. Effect of cultivation on root extent of osage orange. 



It must be seen from these figures that where the ground adjacent 

 to windbreaks is not cultivated at all the roots will gain possession 

 of a much larger area than where one or both sides are cultivated. 



(6) The presence of other trees competing with those on the edge 

 of the windbreak for the soil moisture. Trees on the edge of a grove 

 will have practically a one-sided root system, and this, of course, 

 must be more extensive, in the direction in which moisture is easily 

 found, than the roots of trees in a single row, which extend freely 

 in both directions. 



