GRAPE REGIONS AND THEIR DETERMINANTS 23 



Climate 



Under the assumption, then, that elimate, of all factors, is 

 chief in phiying providence to the grape, let us examine some- 

 what critically the relations of climate to grape-growing. 

 When analyzed, the essentials of climate, as it governs grape- 

 growing, are found to be six : first, length of season ; second, 

 seasonal sum of heat ; third, amount of humidity in summer 

 weather; fourth, dates of spring and autumn frosts; fifth, 

 winter temperature ; sixth, air currents. 



Length of season. 



To reach true perfection, each grape variety has a length of 

 season of its own. With each, if it is grown in too low a lati- 

 tude, the vine is uninterrupted in growth ; its leaves tend to 

 become evergreen; and not infrequently it produces at the 

 same time blossoms, green fruits and ripe fruits. This is, of 

 course, the extreme to which grapes pass in the far South. 

 Again, many northern varieties fail where southern grapes 

 succeed because the fruits pass too rapidly from maturity to 

 decay. On the other hand, very often southern grapes are 

 hardy in vine in the North, but the season is not sufficiently 

 long for the fruit to mature and to acquire sufficient sugar to 

 give them good keeping quality, properly to pass through 

 vinous fermentation, or even to make a good unfermented 

 grape-juice. In the uneven topography of this continent, it is 

 not possible to state the range in latitude in which grapes can 

 be cultivated to advantage, for latitude is often set aside by 

 altitude. Thus, isothermal lines, or lines of ec^ual temperature, 

 are much curved in America and do not at all coincide with the 

 parallels of latitude. 



Other factors, of course, than length of season enter into the 

 ripening of grapes. The daily range in temperature, not al- 

 ways dependent on latitude, affects ripening. Cool nights may 



