The vine is far more tolerant of cold than the olive, but to
produce tolerable wine it demands, at the season of ripening, a
degree of heat not much less than that needed by the more delicate
tree. These conditions are satisfied in the deeper valleys
of the Alps, even in the interior of the chain, and up to a
considerable height on slopes exposed to the sun. The protection
afforded by winter snow enables the plant to resist severe
and prolonged frosts, such as would be fatal in more exposed
situations. Many wild plants characteristic of the warmer
parts of middle Europe are seen to flourish along with the
vine. A mean summer temperature of at least 20C (68°F) is considered
necessary to produce tolerable wine, but in ordinary seasons
this is much exceeded in many of the great valleys of the Alps.
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