Sorrento Lemons are locally selected forms of the Feminello variety. These selections are sometimes known as 'Ovale di Sorrento' and 'Sfusato Amalfitano', although the grower I spoke to only knew his lemons as Feminello.
The lemon groves require protection  from cold winter winds, rain, hail and occasional frost. Tall wooden frames are built and sides and roof were traditionally covered in a kind of rush, twig or bamboo matting. Today black polythene mesh sheeting is being used extensively as a replacement. 
The Sorrento peninsular, south of Naples (Italy), is famous for its lemons. Surprisingly, other citrus varieties do not seem to be commercially viable, although individual trees are not uncommon. Citrons are produced about 200kms futher south along the Calabrian coast, and the best Italian oranges are from the island of Sicily. 
During a family holiday in the Sorrento area at Easter 2004, I managed to sneak in a little citrus watching!
The lemon groves often cascade down terraces towards the sea.
Here are examples of the old and new style weather protection systems.
Older trees are very tall, perhaps 8m (25ft) and require long ladders for picking. Lower branches and ripening fruit are supported on an internal wooden frame. On cloudy days it is surprisingly dim  inside the grove shelters.

On the tourist routes around the Sorrento peninsular and outside the gates of nearby Pompei, vendors set up their eye-catching citrus stalls to attract the passing trade. They include huge Diamante citrons and Tarocco blood oranges from further south. Some stalls also sell the local lemon liqueur 'limoncello'.
I couldn't resist buying these two huge fruits,  a citron and a lemon. Both measured a full 6" (15cms) long. They also had stems attached, which I will try to propagate from! The stall holder incorrectly described the citron as a grapefruit/lime cross, but did say it was called 'cedro' in Italian. This is indeed the word for citron, Citrus medica.
page re-built 11th June 2009