GROWING SEASON TEMPERATURES 



239 



Stillwater, Okla., 967; Parry, N. J., 909; State College, Pa., 725; Burling- 

 ton, Vt., 577. 



Table 3. 



-Heat Units to the Date of Ripening of Elberta Peach at Various 

 Points and Total Heat Units for the Year 



In Chestnut Blight. — Stevens has made an interesting application of these 

 various constants to studies of the growth of tlie chestnut blight fungus. Assum- 

 ing 45°F. as the lowest effective temperature, he compares the summations of 

 temperatures above that point at various localities with the observed growth of 

 the blight cankers and finds that "the temperature summation falls off somewhat 

 more rapidly northward than does the amount of growth." In a later paper he 

 reports that the summations on the "Physiological basis" do not fit the observed 

 growth so well as the summations of remainder or exponential indices. ^^^' ^^^ 



Variations in Heat Requirements from Season to Season. — Sand- 

 sten^^^ made a study of heat units accumulating at blossom time for the 

 apple and plum during several seasons at Madison, Wis. As appears from 

 Table 4, composed of items taken from his data, he found considerable 

 variation from year to year and from variety to variety. Combining 



Table 4. — Number of Positive Temperature Units (above 32°F.) Receh^ed 

 Each Year from Jan. 1 to the Date of Fir.st Bloom 



