84 



INTERNATIONAL CONGRESS OF VITICULTURE 



Seasonal Sum of Heat. 



According to the observations of A. Angot* the buds of the vine com- 

 mence to start when the mean daily temperature reaches 9C. From this 

 point until the ripening of the grapes, the sum of the mean daily tempera- 

 tures above 9 C. must reach 1130 C. for the earliest varieties and 1520 

 for the latest. 



In the accompanying diagram, drawn from data in the reports of the 

 United States Weather Bureau, the seasonal sum of heat for various typical 

 localities is shown graphically. This sum is indicated by a line drawn 

 through points which represent the mean temperatures of every month where 

 these temperatures exceed 48 F. (9 C). Two vertical dashes drawn through 

 this line indicate the average dates of ripening for the earliest, and for the 

 latest varieties according to the data of Angot. Crosses represent the dates 

 of the latest spring frost and of the earliest autumn frost and also the mean 

 dates for both of these frosts where records are available. 



Locality Rainfall 



Sissons, elevation, 3555 ft 37.8 in. 



Redding, Sacramento Valley 36.2 in. 



Stockton, Sacramento Valley 15.5 in. 



Merced, San Joaquin Valley 10.3 in. 



Bakersfield, San Joaquin Valley, 4.8 in. 



Salton, Coachella Valley 2.5 in. 



Ukiah, Coast Range 35.0 in. 



Napa, Coast Range 23.7 in. 



Redlands, Coast Range 14.8 in. 



Eureka, Pacific Littoral 45.8 in. 



Berkeley, Pacific Littoral 26.5 in. 



Raleigh, North Carolina.... .. 49.9 in. 



Seasonal 



Sum of Heat above 9 C. 



Apr. to Oct. 2331 F. 1295 C. 



Feb. to Nov. 5538 F.=3077 C. 



Feb. to Nov. 4553 F.=2529 C 



Feb. to Nov. 5592 F.=3107 C. 



Feb. to Nov. 6783 F. 3768 C. 



Dec. to Nov.10310 F. =5728 C. 



Mar. to Nov. 3703 F.=2057 C. 



Feb. to Nov. 3300 F. 1833 C. 



Dec. to Nov. 5750 F.=3195 C. 



Apr. to Nov. 1406 F.= 770 C. 



Feb. to Nov. 2842 F. =1579 C. 



Mar. to Nov. 4822 F.=2679 C. 



This diagram indicates that the data given by Angot do not apply pre- 

 cisely to California. In all cases, the actual dates of ripening are from 2 to 4 

 weeks later than is required by the theory. The greater differences are in 

 the hotter localities. In the Coachella Valley, for example, represented by the 

 record for Salton, grapes should ripen, according to the theory, from May 3 

 to May 23. Actually the earliest varieties ripen there about May 15 to 30 

 and the latest about June 15 to 30. For Napa the diagram shows August 12 

 to September 24 as the dates of ripening. The actual mean dates are about 

 from September 1 to October 15. Undoubtedly other factors enter into the 

 result. It may be that the daily range of temperature affects the rate of 

 ripening. Delay, due to the cool nights of the Californian summer, may 

 counteract the acceleration due to the hot days. It may be, also, that in the 

 hottest regions the temperature of maximum acceleration is passed. The last 

 increments of heat at Bakersfield and Salton, while undoubtedly hastening 

 the ripening, may do so to a less extent than equal increments at lower 

 temperatures. 



* Etudes sur les vendanges en France (Annales du Bureau central me"teor- 

 logique, 1883). See also, Viala & Vermorel, "Ampelographie" T. I. p. 636. 



