34 



WINDBREAKS. 



interest to determine the extent of these roots and the area which 

 may be so seriously affected in the driest years by different species. 

 The soil surveys previously described indicate the limits of the 

 tree roots, in some instances by the depression of the moisture curve 

 at the tips of the roots and in all cases by the sudden increase in 

 moisture when the ends of the roots are passed. The point farthest 

 from the trees, where there was appreciable depletion of the moisture, 

 has been accepted as the limit of the tree roots. Table 4 indicates 

 the root extent of all species studied in distances at right angles to 

 the windbreaks concerned. 



TABLE 4. Average root extent of Carious species in windbreaks. 



From the data given it is evident that, contrary to the common 

 opinion, cottonwood has the least extensive roots of any of the broad- 

 leaf species, and hence has the least power for damage to crops in 

 dry years. Next in order come green ash, osage orange, and mul- 

 berry. The data given for honey locust are too meager to form the 

 basis of any good estimate of its sapping powers. Of the conifers, 

 white pine shows a distinctly compact root system, while Scotch 

 and Austrian pines are, in the situations studied and habitually, 

 much longer rooted. The figures given for the last two species are 



