RESULTS OF MEASUREMENTS. 



61 



of evaporation is appreciable even in the minimum temperatures as 

 registered by thermometers which expose only a very small surface 

 to Ijie wind; it would be even more marked with thin objects like 

 leaves which have a very large surface in proportion to their volume. 

 (8) It is probable that the effect of a windbreak at night is always 

 beneficial in checking evaporation from and cooling of leaves in the 

 protected zone. 



A . 

 S2.8 



SI.8 

 S0.3 

 43.6 



4s.a' 



47J 

 S3.4 

 57.4 

 S6.4 

 Sf.4 

 63.3 

 62J 

 6>.3 

 60.J 



// 



DIAGRAM 29. Influence of cottonwood belt on nocturnal cooling of air, under various conditions of 

 sky and wind movement. Wind in miles per hour; temperature in degrees F. 



(9) The daily superheating of the air amounts to about the same 

 number of degrees whether the temperature outside the protected 

 zone be high or low, but as expressed in percentages of the total heat 

 available for plant growth, it is most important in the spring and fall, 

 when the supply is lowest. (See diagrams 26 and 27.) 



