RESULTS OF MEASUREMENTS. 

 TABLE 2. Branching extent of various trees Continued. 



23 



The relative shading qualities of the several species are iMre clearl^ 

 shown by the curves on diagrams 2 to 6, inclusive. The^shaded ai 

 of the diagrams show the entire volume of light cui-^ff froi 

 ground. It will be seen that the high branching of cotton woo< 

 maple permits the entrance of considerable light to the ground4it 

 base of the trees, while the low, spreading branches of locust and os* 

 orange create under the tree a zone in which the growth of smaller 

 plants is quite impossible. This difference between species is especi- 

 ally marked in north-south windbreaks, for the morning and after\^ 

 noon sun may shine under the branches unless the} r are very low. 



Orientation. Of greater importance than the difference between 

 the various species in their shading effect is the difference between 

 orientations. Table 1 shows that the amount of light used by the 

 trees in the north-south row is considerably in excess of that taken up 

 by the trees in a row whose orientation is east-west, and the diagrams 

 show that this shading is not only greater in volume, but greater in 

 extent. This is, of course, due to the fact that the north-south wind- 

 break receives sunlight from one side or the other during about two- 

 thirds of the day, while in the east- west row, especially in midsummer, 

 the shadows fall little outside the area covered by the branches. 

 Crops adjacent to a north-south windbreak will, therefore, suffer more 

 from the shading than those adjacent to an east-west windbreak. 



