ASPECT. 27 



and when once cleared tree .m'mvth is often difficult to renew. 

 As proof of the importance of these conditions as affecting tree 

 growth \ve have the commonly observed fact that the south 

 and west sides of steep hills and mountains are more likely to 

 be bare than any others. This can be very plainly seen on the 

 bluffs along the Mississippi River in Minnesota. 



A Western Slope receives the sun's rays obliquely, but in 

 the warmest part of the day, and in this section gets the full 

 force of our hot dry southwest winds. The effect of such an 

 exposure on growth is about the same as the southern slope. 



