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The great plain of Upper Italy has a winter climate colder than that of the British
Islands. The olive and the characteristic shrubs
of the northern coasts of the Mediterranean do not thrive in the open
air, but the former valuable tree ripens its fruit in sheltered places at the foot of the mountains, and penetrates along the
deeper valleys and the shores of the Italian lakes.
The evergreen oak is wild on the rocks about the Lake of Garda, and lemons are cultivated on a large scale, with
partial protection in winter. The olive has been known to survive severe cold when of short duration, but it cannot be cultivated
with success where frosts are prolonged, or where the mean winter temperature falls below 5.5C (42°F); and to produce fruit it
requires a heat of at least 24C (75°F) during the day, continued through four or five months of the summer and autumn.
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