342 



FUNDAMENTALS OF FRUIT PRODUCTION 



not prevent radiation but it mixes the air and prevents excessive cooling 

 of any small portion of it; therefore, windy nights are not likely to be 

 frosty. It is the nights which combine good radiation conditions with 

 still air that the fruit grower should watch when his trees are in bloom. 



INFLUENCE OF LOCATION ON DANGER FROM FROST 



It has been shown that in the northern hemisphere the blossoming of 

 fruit trees begins early in the south and, subject of course to minor dif- 

 ferences, moves northward at a rate of 4 or 5 days for each degree of lati- 

 tude, though somewhat more rapidly to the west of a given point than to 

 the east. If the date of the last killing frost in the spring moved north- 

 ward at the same rate, the calculation of the chances of a given fruit's 

 escaping frost at any location would be a simple matter. Unfortunately 



Fig. 32. — The blossoming season of Wildgoose plum for 1898. (After Waugh'^^*) 



conditions are much more complicated. Dates of blossoming and of 

 last frosts fluctuate from year to year. There are local variations 

 particularly in the occurrence and severity of frosts; these are considered 

 later. The present phase of the discussion is intended to point out that 

 certain regions are more subject, perhaps, to late frosts at critical times 

 for the fruit grower than other localities. 



The Blossoming Season and Latitude. — Figure 32 shows the dates of 

 blossoming for the Wildgoose plum at various points in the United States 

 for 1898, a season that was, on the whole, rather earlier than the average. ^"^ 

 Unfortunately not enough data are available for the construction of a 

 map showing average blossoming seasons for any particular variety of 

 fruit and minor fluctuations due to varying weather in different sections 



