244 POMOLOGY 



keeping quality is very largely dependent on the warmth 

 and length of the growing season. This may be measured 

 with fair satisfaction for the apple-growing regions of 

 North America by an average of the mean temperatures 

 for the months of March to September, inclusive. This is 

 called the mean summer temperature, and gives tempera- 

 tures ranging from 52° to 72° F. 



"The factors determining the mean suimner temperature 

 in a given orchard are (1) latitude, (2) elevation, (3) site 

 and aspect, (4) soil, (5) culture, (6) prevailing winds, (7) 

 sunshine. 



''A departure of over 2° from the optimum mean for a given 

 variety will result in less desirable fruit, though this may 

 not be marked in short season varieties. 



"A summer mean too low for a variety results in (1) 

 greater acidity, (2) increased insoluble solids, (3) greater 

 astringency, (4) less coloration, (5) decreased size, (6) 

 scalding in storage. 



"A summer mean too high for a variety results in (1) 

 uneven ripening, (2) premature dropping, (3) rotting on 

 the trees, (4) poor keeping quality, (5) lack of flavor, (6) 

 'mealiness,' (7) less intense color, (8) decreased size." 



213. Specific requirements for certain varieties.^ — It 

 seems to be established, as above stated, that a variet}^ of 

 fruit has a certain optimum temperature at which it thrives 

 best, but this has not been determined for all varieties. Win- 

 slow ^ has contributed some interesting figures on the length 

 of growing season required by some varieties of apples 

 grown in the Northwest. The "length of growing season" 

 is described by him as the number of days between killing 

 frosts, or more accurately the period during which the mean 

 temperature is over 43° F. He also uses the number of 

 "heat units" during the growing season as a guide in the 

 1 Winslow, R. M. Amer. Soc. Hort. Sci. 1914. 



