The mistletoe clouds are usually spaced pretty evenly through the tree, growing straight out of the bark. They look like the growths pushing through the skin of the Elephant Man, erupting from inside, the bark stretching to start with, but the parasite breaking through eventually to form its own green twigs and sycamore-seed-head-like pairs of leaves. These are thick and leathery, some a dullish green, others more acid, with yellow mixed in.  Mistletoe flowers from February to April, with very small, inconspicuous, four-petalled sprigs, but it's the berries - from November into the New Year - that make it interesting.  You'll see a mix of berried and unberried bunches in a tree - the male without the berry, the females packed with their poisonous fruit. If chunks fall on the ground after a storm and sheep have a good graze, the ewes may abort their lambs.  The berries look like dull pearls or white currants, blue-white, rather than creamy-green, and they're incredibly sticky. Squeeze one between finger and thumb and then try to drop it and you can't - they're as tacky as chewing gum when you're trying to put it in the bin.  That's how it is spread. The birds eat the berries, which are so sticky they have to wipe their beaks on the tree branches, and so deposit the seeds.  There are about 900 members of the mistletoe family worldwide, and most are found in the tropics. Viscum album is the only species growing wild in Britain. Our mistletoe really likes cider apple trees, slightly weatherworn and 40 to 50 years old.  It doesn't grow so well on Bramleys and won't thrive at all on most dessert apple trees. Nor did I see it on a single oak. That's why there's so much of it in this part of the world, traditional cider country of Somerset, Gloucestershire, Herefordshire and Worcestershire.  Mistletoe has been gradually on the increase over the past 20 years and seems to benefit from global warming. This year, in particular, there's more than usual after a wet August. The moisture gave it extra fruiting vigour and there are more berries on every bunch.  But there were warnings from some conservationists this week, that mistletoe may become scarce, or even vanish, in the next 10 to 20 years.  At least 60 per cent of our orchards have disappeared since the 1950s, prompting fears of a knock-on effect on the mistletoe and the need for more pricey European imports. The National Trust is behind a new campaign to prompt orchard growers and gardeners to nurture the plant.  "Fast forward 10 or 20 years, and the orchards won't be there," says environmental consultant Jonathan Briggs, a mistletoe expert. "A Christmas kiss could become more expensive."  This Tuesday, the auction in Tenbury Wells will be in full flow again, but the recent cold snap has meant that fewer farmers and travellers - Romany gipsies often cut down mistletoe - bringing less into the market than usual.  To harvest, you have to get up and into the tree. Mike Adams, a farmer from Eastham Bridge, told me he uses a front loader on his tractor, with someone standing in it to cut down the mistletoe, or he'll shimmy up a ladder and then carefully sever the branch with the mistletoe on it.  I had never realised it before - seeing the bunches in shops already stripped right down - but with most of the harvest, you have to remove a small chunk of the host tree branches as well as the mistletoe itself.  The wood is sawn out with the bunches sprouting straight from it. Take too much, or remove wood from the middle of the tree, and you risk killing it.  Although most mistletoe for sale at Christmas is imported from northern France, Tenbury Wells is the place to get the home-grown stuff.  The auction used to take place in the livestock mart in the centre of town, but the mart is now shut and another Tesco is likely to occupy the site. To find your mistletoe, head to a field in the business park on the outskirts of the town.  It has the feel of a county agricultural show - lots of trailers, vans and Land Rovers, with the punters, mainly men, walking around on muddy trackways in the freezing cold checking out what's on offer.  The wraps of mistletoe, priced between £15 and £20, are laid out on the ground, each one tied and labelled with the name of the picker.  These nurserymen, and buyers from garden centres and farm shops, buy in bulk and strip down bunches, breaking them into single stems before selling them on for a healthy markup.  Anyone can join in, although every buyer must pay a £3 registration fee and have a bidder's number. We met a group from Ireland, who were taking a van load of mistletoe back to sell on the streets of Cork; a couple from Scotland, and a man from Wales, who runs a mistletoe stall in Swansea.  The buying-and-selling throng last month when I attended the auction prove that, despite conservationists' warnings that mistletoe is on the wane, its popularity clearly is not.  Make sure you buy some this Christmas - and make it home-grown mistletoe if you can. It's not just good for kissing - it's good for Britain, too.  • Buy a bunch of mistletoe picked from Mike and Celia Adams's Worcestershire orchard; www.temework.co.uk; £12 including p&p. Last orders by Friday, December 17.  Buy mistletoe at gardenshop.telegraph.co.uk Buy Christmas trees at gardenshop.telegraph.co.uk
Sarah Raven visits Britain's busiest mistletoe market - and discovers that   recent weather conditions have created a bumper crop this year.