ORCHARD PROTECTION. 69 



the case with th^ apple, pear, strawberry and most cultivated 

 northern fruits. 



We also have fruit plants like that of the Buffalo Berry 

 and Juneberry whose flowers are seldom injured by severe frosts, 

 even if fully -expanded at the time it occurs. 



The pistils are the parts of flowers most easily Injured. — 

 Thus, in the strawberry, after a severe frost in flowering time, 

 we will often find the pistils ruined but the stamens apparently 

 uninjured. 



When injurious frosts are most likely to occur. — Injurious 

 frosts are most likely to occur in places where the air is still, 

 especially in low spots where the air is not only still but where 

 the cold air from the surrounding elevations drains in. If the 

 air moves rapidly, the warm air is mixed with the cold air and 

 does not separate. Such frosty places are evident at the time 

 of the first s-evere autumn frosts, especially if this comes early. 

 It will then be seen that the frosty air fills certain hollows, as 

 water might fill it. In such places, often called warm sheltered 

 nooks, winter killing is frequently serious. A windbreak miay 

 also make a frost pocket on the side hill by interfering with 

 the free circulation of the air. 



The locations where injurious frosts are least likely to oc- 

 cur and hence afford the best location for fruit growing are high 

 elevations tipping to the north or east where growth is rather 

 backward in spring. Other locations that are comparatively 

 exempt from injurious frosts are such as are near lakes or 

 streams which tend to produce an equable climate. 



Foretelling of frosts. — Frosts may be foretold some hours 

 in advance by means of the wet and dry-bulb thermometers, 

 the readings of which are compared. The difference between 

 the readings is due to the evaporation from the wet bulb ther- 

 mometer which produces a degree of cold in a direct ratio ac- 

 cording to the dryness of the air. If the air is very dry, the 

 wet bulb thermometer may record ten or fifteen degrees lower 

 than the dry bulb. If the air is saturated with moisture they 

 will read exactly alike. The basis for the calculation is the 

 fact that we seldom have injurious early autumn or late spring 

 frosts after the dew begins to fall. By referring the difference 



